///*
// * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
// *
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//
///*
// *
// *
// *
// *
// *
// * Written by Doug Lea with assistance from members of JCP JSR-166
// * Expert Group and released to the public domain, as explained at
// * http://creativecommons.org/publicdomain/zero/1.0/
// */
//
//package com.xiaolyuh;
//
//import java.io.ObjectStreamField;
//import java.io.Serializable;
//import java.lang.reflect.ParameterizedType;
//import java.lang.reflect.Type;
//import java.util.AbstractMap;
//import java.util.Arrays;
//import java.util.Collection;
//import java.util.Enumeration;
//import java.util.HashMap;
//import java.util.Hashtable;
//import java.util.Iterator;
//import java.util.Map;
//import java.util.NoSuchElementException;
//import java.util.Set;
//import java.util.Spliterator;
//import java.util.concurrent.ConcurrentMap;
//import java.util.concurrent.CountedCompleter;
//import java.util.concurrent.ForkJoinPool;
//import java.util.concurrent.ThreadLocalRandom;
//import java.util.concurrent.atomic.AtomicReference;
//import java.util.concurrent.locks.LockSupport;
//import java.util.concurrent.locks.ReentrantLock;
//import java.util.function.BiConsumer;
//import java.util.function.BiFunction;
//import java.util.function.Consumer;
//import java.util.function.DoubleBinaryOperator;
//import java.util.function.Function;
//import java.util.function.IntBinaryOperator;
//import java.util.function.LongBinaryOperator;
//import java.util.function.ToDoubleBiFunction;
//import java.util.function.ToDoubleFunction;
//import java.util.function.ToIntBiFunction;
//import java.util.function.ToIntFunction;
//import java.util.function.ToLongBiFunction;
//import java.util.function.ToLongFunction;
//import java.util.stream.Stream;
//
///**
// * A hash table supporting full concurrency of retrievals and
// * high expected concurrency for updates. This class obeys the
// * same functional specification as {@link java.util.Hashtable}, and
// * includes versions of methods corresponding to each method of
// * {@code Hashtable}. However, even though all operations are
// * thread-safe, retrieval operations do <em>not</em> entail locking,
// * and there is <em>not</em> any support for locking the entire table
// * in a way that prevents all access.  This class is fully
// * interoperable with {@code Hashtable} in programs that rely on its
// * thread safety but not on its synchronization details.
// *
// * <p>Retrieval operations (including {@code get}) generally do not
// * block, so may overlap with update operations (including {@code put}
// * and {@code remove}). Retrievals reflect the results of the most
// * recently <em>completed</em> update operations holding upon their
// * onset. (More formally, an update operation for a given key bears a
// * <em>happens-before</em> relation with any (non-null) retrieval for
// * that key reporting the updated value.)  For aggregate operations
// * such as {@code putAll} and {@code clear}, concurrent retrievals may
// * reflect insertion or removal of only some entries.  Similarly,
// * Iterators, Spliterators and Enumerations return elements reflecting the
// * state of the hash table at some point at or since the creation of the
// * iterator/enumeration.  They do <em>not</em> throw {@link
// * java.util.ConcurrentModificationException ConcurrentModificationException}.
// * However, iterators are designed to be used by only one thread at a time.
// * Bear in mind that the results of aggregate status methods including
// * {@code size}, {@code isEmpty}, and {@code containsValue} are typically
// * useful only when a map is not undergoing concurrent updates in other threads.
// * Otherwise the results of these methods reflect transient states
// * that may be adequate for monitoring or estimation purposes, but not
// * for program control.
// *
// * <p>The table is dynamically expanded when there are too many
// * collisions (i.e., keys that have distinct hash codes but fall into
// * the same slot modulo the table size), with the expected average
// * effect of maintaining roughly two bins per mapping (corresponding
// * to a 0.75 load factor threshold for resizing). There may be much
// * variance around this average as mappings are added and removed, but
// * overall, this maintains a commonly accepted time/space tradeoff for
// * hash tables.  However, resizing this or any other kind of hash
// * table may be a relatively slow operation. When possible, it is a
// * good idea to provide a size estimate as an optional {@code
// * initialCapacity} constructor argument. An additional optional
// * {@code loadFactor} constructor argument provides a further means of
// * customizing initial table capacity by specifying the table density
// * to be used in calculating the amount of space to allocate for the
// * given number of elements.  Also, for compatibility with previous
// * versions of this class, constructors may optionally specify an
// * expected {@code concurrencyLevel} as an additional hint for
// * internal sizing.  Note that using many keys with exactly the same
// * {@code hashCode()} is a sure way to slow down performance of any
// * hash table. To ameliorate impact, when keys are {@link Comparable},
// * this class may use comparison order among keys to help break ties.
// *
// * <p>A {@link Set} projection of a ConcurrentHashMap may be created
// * (using {@link #newKeySet()} or {@link #newKeySet(int)}), or viewed
// * (using {@link #keySet(Object)} when only keys are of interest, and the
// * mapped values are (perhaps transiently) not used or all take the
// * same mapping value.
// *
// * <p>A ConcurrentHashMap can be used as scalable frequency map (a
// * form of histogram or multiset) by using {@link
// * java.util.concurrent.atomic.LongAdder} values and initializing via
// * {@link #computeIfAbsent computeIfAbsent}. For example, to add a count
// * to a {@code ConcurrentHashMap<String,LongAdder> freqs}, you can use
// * {@code freqs.computeIfAbsent(k -> new LongAdder()).increment();}
// *
// * <p>This class and its views and iterators implement all of the
// * <em>optional</em> methods of the {@link Map} and {@link Iterator}
// * interfaces.
// *
// * <p>Like {@link Hashtable} but unlike {@link HashMap}, this class
// * does <em>not</em> allow {@code null} to be used as a key or value.
// *
// * <p>ConcurrentHashMaps support a set of sequential and parallel bulk
// * operations that, unlike most {@link Stream} methods, are designed
// * to be safely, and often sensibly, applied even with maps that are
// * being concurrently updated by other threads; for example, when
// * computing a snapshot summary of the values in a shared registry.
// * There are three kinds of operation, each with four forms, accepting
// * functions with Keys, Values, Entries, and (Key, Value) arguments
// * and/or return values. Because the elements of a ConcurrentHashMap
// * are not ordered in any particular way, and may be processed in
// * different orders in different parallel executions, the correctness
// * of supplied functions should not depend on any ordering, or on any
// * other objects or values that may transiently change while
// * computation is in progress; and except for forEach actions, should
// * ideally be side-effect-free. Bulk operations on {@link java.util.Map.Entry}
// * objects do not support method {@code setValue}.
// *
// * <ul>
// * <li> forEach: Perform a given action on each element.
// * A variant form applies a given transformation on each element
// * before performing the action.</li>
// *
// * <li> search: Return the first available non-null result of
// * applying a given function on each element; skipping further
// * search when a result is found.</li>
// *
// * <li> reduce: Accumulate each element.  The supplied reduction
// * function cannot rely on ordering (more formally, it should be
// * both associative and commutative).  There are five variants:
// *
// * <ul>
// *
// * <li> Plain reductions. (There is not a form of this method for
// * (key, value) function arguments since there is no corresponding
// * return type.)</li>
// *
// * <li> Mapped reductions that accumulate the results of a given
// * function applied to each element.</li>
// *
// * <li> Reductions to scalar doubles, longs, and ints, using a
// * given basis value.</li>
// *
// * </ul>
// * </li>
// * </ul>
// *
// * <p>These bulk operations accept a {@code parallelismThreshold}
// * argument. Methods proceed sequentially if the current map size is
// * estimated to be less than the given threshold. Using a value of
// * {@code Long.MAX_VALUE} suppresses all parallelism.  Using a value
// * of {@code 1} results in maximal parallelism by partitioning into
// * enough subtasks to fully utilize the {@link
// * ForkJoinPool#commonPool()} that is used for all parallel
// * computations. Normally, you would initially choose one of these
// * extreme values, and then measure performance of using in-between
// * values that trade off overhead versus throughput.
// *
// * <p>The concurrency properties of bulk operations follow
// * from those of ConcurrentHashMap: Any non-null result returned
// * from {@code get(key)} and related access methods bears a
// * happens-before relation with the associated insertion or
// * update.  The result of any bulk operation reflects the
// * composition of these per-element relations (but is not
// * necessarily atomic with respect to the map as a whole unless it
// * is somehow known to be quiescent).  Conversely, because keys
// * and values in the map are never null, null serves as a reliable
// * atomic indicator of the current lack of any result.  To
// * maintain this property, null serves as an implicit basis for
// * all non-scalar reduction operations. For the double, long, and
// * int versions, the basis should be one that, when combined with
// * any other value, returns that other value (more formally, it
// * should be the identity element for the reduction). Most common
// * reductions have these properties; for example, computing a sum
// * with basis 0 or a minimum with basis MAX_VALUE.
// *
// * <p>Search and transformation functions provided as arguments
// * should similarly return null to indicate the lack of any result
// * (in which case it is not used). In the case of mapped
// * reductions, this also enables transformations to serve as
// * filters, returning null (or, in the case of primitive
// * specializations, the identity basis) if the element should not
// * be combined. You can create compound transformations and
// * filterings by composing them yourself under this "null means
// * there is nothing there now" rule before using them in search or
// * reduce operations.
// *
// * <p>Methods accepting and/or returning Entry arguments maintain
// * key-value associations. They may be useful for example when
// * finding the key for the greatest value. Note that "plain" Entry
// * arguments can be supplied using {@code new
// * AbstractMap.SimpleEntry(k,v)}.
// *
// * <p>Bulk operations may complete abruptly, throwing an
// * exception encountered in the application of a supplied
// * function. Bear in mind when handling such exceptions that other
// * concurrently executing functions could also have thrown
// * exceptions, or would have done so if the first exception had
// * not occurred.
// *
// * <p>Speedups for parallel compared to sequential forms are common
// * but not guaranteed.  Parallel operations involving brief functions
// * on small maps may execute more slowly than sequential forms if the
// * underlying work to parallelize the computation is more expensive
// * than the computation itself.  Similarly, parallelization may not
// * lead to much actual parallelism if all processors are busy
// * performing unrelated tasks.
// *
// * <p>All arguments to all task methods must be non-null.
// *
// * <p>This class is a member of the
// * <a href="{@docRoot}/../technotes/guides/collections/index.html">
// * Java Collections Framework</a>.
// *
// * @since 1.5
// * @author Doug Lea
// * @param <K> the type of keys maintained by this map
// * @param <V> the type of mapped values
// */
//public class ConcurrentHashMap18<K,V> extends AbstractMap<K,V>
//        implements ConcurrentMap<K,V>, Serializable {
//    private static final long serialVersionUID = 7249069246763182397L;
//
//    /*
//     * Overview:
//     *
//     * The primary design goal of this hash table is to maintain
//     * concurrent readability (typically method get(), but also
//     * iterators and related methods) while minimizing update
//     * contention. Secondary goals are to keep space consumption about
//     * the same or better than java.util.HashMap, and to support high
//     * initial insertion rates on an empty table by many threads.
//     *
//     * This map usually acts as a binned (bucketed) hash table.  Each
//     * key-value mapping is held in a Node.  Most nodes are instances
//     * of the basic Node class with hash, key, value, and next
//     * fields. However, various subclasses exist: TreeNodes are
//     * arranged in balanced trees, not lists.  TreeBins hold the roots
//     * of sets of TreeNodes. ForwardingNodes are placed at the heads
//     * of bins during resizing. ReservationNodes are used as
//     * placeholders while establishing values in computeIfAbsent and
//     * related methods.  The types TreeBin, ForwardingNode, and
//     * ReservationNode do not hold normal user keys, values, or
//     * hashes, and are readily distinguishable during search etc
//     * because they have negative hash fields and null key and value
//     * fields. (These special nodes are either uncommon or transient,
//     * so the impact of carrying around some unused fields is
//     * insignificant.)
//     *
//     * The table is lazily initialized to a power-of-two size upon the
//     * first insertion.  Each bin in the table normally contains a
//     * list of Nodes (most often, the list has only zero or one Node).
//     * Table accesses require volatile/atomic reads, writes, and
//     * CASes.  Because there is no other way to arrange this without
//     * adding further indirections, we use intrinsics
//     * (sun.misc.Unsafe) operations.
//     *
//     * We use the top (sign) bit of Node hash fields for control
//     * purposes -- it is available anyway because of addressing
//     * constraints.  Nodes with negative hash fields are specially
//     * handled or ignored in map methods.
//     *
//     * Insertion (via put or its variants) of the first node in an
//     * empty bin is performed by just CASing it to the bin.  This is
//     * by far the most common case for put operations under most
//     * key/hash distributions.  Other update operations (insert,
//     * delete, and replace) require locks.  We do not want to waste
//     * the space required to associate a distinct lock object with
//     * each bin, so instead use the first node of a bin list itself as
//     * a lock. Locking support for these locks relies on builtin
//     * "synchronized" monitors.
//     *
//     * Using the first node of a list as a lock does not by itself
//     * suffice though: When a node is locked, any update must first
//     * validate that it is still the first node after locking it, and
//     * retry if not. Because new nodes are always appended to lists,
//     * once a node is first in a bin, it remains first until deleted
//     * or the bin becomes invalidated (upon resizing).
//     *
//     * The main disadvantage of per-bin locks is that other update
//     * operations on other nodes in a bin list protected by the same
//     * lock can stall, for example when user equals() or mapping
//     * functions take a long time.  However, statistically, under
//     * random hash codes, this is not a common problem.  Ideally, the
//     * frequency of nodes in bins follows a Poisson distribution
//     * (http://en.wikipedia.org/wiki/Poisson_distribution) with a
//     * parameter of about 0.5 on average, given the resizing threshold
//     * of 0.75, although with a large variance because of resizing
//     * granularity. Ignoring variance, the expected occurrences of
//     * list size k are (exp(-0.5) * pow(0.5, k) / factorial(k)). The
//     * first values are:
//     *
//     * 0:    0.60653066
//     * 1:    0.30326533
//     * 2:    0.07581633
//     * 3:    0.01263606
//     * 4:    0.00157952
//     * 5:    0.00015795
//     * 6:    0.00001316
//     * 7:    0.00000094
//     * 8:    0.00000006
//     * more: less than 1 in ten million
//     *
//     * Lock contention probability for two threads accessing distinct
//     * elements is roughly 1 / (8 * #elements) under random hashes.
//     *
//     * Actual hash code distributions encountered in practice
//     * sometimes deviate significantly from uniform randomness.  This
//     * includes the case when N > (1<<30), so some keys MUST collide.
//     * Similarly for dumb or hostile usages in which multiple keys are
//     * designed to have identical hash codes or ones that differs only
//     * in masked-out high bits. So we use a secondary strategy that
//     * applies when the number of nodes in a bin exceeds a
//     * threshold. These TreeBins use a balanced tree to hold nodes (a
//     * specialized form of red-black trees), bounding search time to
//     * O(log N).  Each search step in a TreeBin is at least twice as
//     * slow as in a regular list, but given that N cannot exceed
//     * (1<<64) (before running out of addresses) this bounds search
//     * steps, lock hold times, etc, to reasonable constants (roughly
//     * 100 nodes inspected per operation worst case) so long as keys
//     * are Comparable (which is very common -- String, Long, etc).
//     * TreeBin nodes (TreeNodes) also maintain the same "next"
//     * traversal pointers as regular nodes, so can be traversed in
//     * iterators in the same way.
//     *
//     * The table is resized when occupancy exceeds a percentage
//     * threshold (nominally, 0.75, but see below).  Any thread
//     * noticing an overfull bin may assist in resizing after the
//     * initiating thread allocates and sets up the replacement array.
//     * However, rather than stalling, these other threads may proceed
//     * with insertions etc.  The use of TreeBins shields us from the
//     * worst case effects of overfilling while resizes are in
//     * progress.  Resizing proceeds by transferring bins, one by one,
//     * from the table to the next table. However, threads claim small
//     * blocks of indices to transfer (via field transferIndex) before
//     * doing so, reducing contention.  A generation stamp in field
//     * sizeCtl ensures that resizings do not overlap. Because we are
//     * using power-of-two expansion, the elements from each bin must
//     * either stay at same index, or move with a power of two
//     * offset. We eliminate unnecessary node creation by catching
//     * cases where old nodes can be reused because their next fields
//     * won't change.  On average, only about one-sixth of them need
//     * cloning when a table doubles. The nodes they replace will be
//     * garbage collectable as soon as they are no longer referenced by
//     * any reader thread that may be in the midst of concurrently
//     * traversing table.  Upon transfer, the old table bin contains
//     * only a special forwarding node (with hash field "MOVED") that
//     * contains the next table as its key. On encountering a
//     * forwarding node, access and update operations restart, using
//     * the new table.
//     *
//     * Each bin transfer requires its bin lock, which can stall
//     * waiting for locks while resizing. However, because other
//     * threads can join in and help resize rather than contend for
//     * locks, average aggregate waits become shorter as resizing
//     * progresses.  The transfer operation must also ensure that all
//     * accessible bins in both the old and new table are usable by any
//     * traversal.  This is arranged in part by proceeding from the
//     * last bin (table.length - 1) up towards the first.  Upon seeing
//     * a forwarding node, traversals (see class Traverser) arrange to
//     * move to the new table without revisiting nodes.  To ensure that
//     * no intervening nodes are skipped even when moved out of order,
//     * a stack (see class TableStack) is created on first encounter of
//     * a forwarding node during a traversal, to maintain its place if
//     * later processing the current table. The need for these
//     * save/restore mechanics is relatively rare, but when one
//     * forwarding node is encountered, typically many more will be.
//     * So Traversers use a simple caching scheme to avoid creating so
//     * many new TableStack nodes. (Thanks to Peter Levart for
//     * suggesting use of a stack here.)
//     *
//     * The traversal scheme also applies to partial traversals of
//     * ranges of bins (via an alternate Traverser constructor)
//     * to support partitioned aggregate operations.  Also, read-only
//     * operations give up if ever forwarded to a null table, which
//     * provides support for shutdown-style clearing, which is also not
//     * currently implemented.
//     *
//     * Lazy table initialization minimizes footprint until first use,
//     * and also avoids resizings when the first operation is from a
//     * putAll, constructor with map argument, or deserialization.
//     * These cases attempt to override the initial capacity settings,
//     * but harmlessly fail to take effect in cases of races.
//     *
//     * The element count is maintained using a specialization of
//     * LongAdder. We need to incorporate a specialization rather than
//     * just use a LongAdder in order to access implicit
//     * contention-sensing that leads to creation of multiple
//     * CounterCells.  The counter mechanics avoid contention on
//     * updates but can encounter cache thrashing if read too
//     * frequently during concurrent access. To avoid reading so often,
//     * resizing under contention is attempted only upon adding to a
//     * bin already holding two or more nodes. Under uniform hash
//     * distributions, the probability of this occurring at threshold
//     * is around 13%, meaning that only about 1 in 8 puts check
//     * threshold (and after resizing, many fewer do so).
//     *
//     * TreeBins use a special form of comparison for search and
//     * related operations (which is the main reason we cannot use
//     * existing collections such as TreeMaps). TreeBins contain
//     * Comparable elements, but may contain others, as well as
//     * elements that are Comparable but not necessarily Comparable for
//     * the same T, so we cannot invoke compareTo among them. To handle
//     * this, the tree is ordered primarily by hash value, then by
//     * Comparable.compareTo order if applicable.  On lookup at a node,
//     * if elements are not comparable or compare as 0 then both left
//     * and right children may need to be searched in the case of tied
//     * hash values. (This corresponds to the full list search that
//     * would be necessary if all elements were non-Comparable and had
//     * tied hashes.) On insertion, to keep a total ordering (or as
//     * close as is required here) across rebalancings, we compare
//     * classes and identityHashCodes as tie-breakers. The red-black
//     * balancing code is updated from pre-jdk-collections
//     * (http://gee.cs.oswego.edu/dl/classes/collections/RBCell.java)
//     * based in turn on Cormen, Leiserson, and Rivest "Introduction to
//     * Algorithms" (CLR).
//     *
//     * TreeBins also require an additional locking mechanism.  While
//     * list traversal is always possible by readers even during
//     * updates, tree traversal is not, mainly because of tree-rotations
//     * that may change the root node and/or its linkages.  TreeBins
//     * include a simple read-write lock mechanism parasitic on the
//     * main bin-synchronization strategy: Structural adjustments
//     * associated with an insertion or removal are already bin-locked
//     * (and so cannot conflict with other writers) but must wait for
//     * ongoing readers to finish. Since there can be only one such
//     * waiter, we use a simple scheme using a single "waiter" field to
//     * block writers.  However, readers need never block.  If the root
//     * lock is held, they proceed along the slow traversal path (via
//     * next-pointers) until the lock becomes available or the list is
//     * exhausted, whichever comes first. These cases are not fast, but
//     * maximize aggregate expected throughput.
//     *
//     * Maintaining API and serialization compatibility with previous
//     * versions of this class introduces several oddities. Mainly: We
//     * leave untouched but unused constructor arguments refering to
//     * concurrencyLevel. We accept a loadFactor constructor argument,
//     * but apply it only to initial table capacity (which is the only
//     * time that we can guarantee to honor it.) We also declare an
//     * unused "Segment" class that is instantiated in minimal form
//     * only when serializing.
//     *
//     * Also, solely for compatibility with previous versions of this
//     * class, it extends AbstractMap, even though all of its methods
//     * are overridden, so it is just useless baggage.
//     *
//     * This file is organized to make things a little easier to follow
//     * while reading than they might otherwise: First the main static
//     * declarations and utilities, then fields, then main public
//     * methods (with a few factorings of multiple public methods into
//     * internal ones), then sizing methods, trees, traversers, and
//     * bulk operations.
//     */
//
//    /* ---------------- Constants -------------- */
//
//    /**
//     * The largest possible table capacity.  This value must be
//     * exactly 1<<30 to stay within Java array allocation and indexing
//     * bounds for power of two table sizes, and is further required
//     * because the top two bits of 32bit hash fields are used for
//     * control purposes.
//     */
//    private static final int MAXIMUM_CAPACITY = 1 << 30;
//
//    /**
//     * The default initial table capacity.  Must be a power of 2
//     * (i.e., at least 1) and at most MAXIMUM_CAPACITY.
//     */
//    private static final int DEFAULT_CAPACITY = 16;
//
//    /**
//     * The largest possible (non-power of two) array size.
//     * Needed by toArray and related methods.
//     */
//    static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
//
//    /**
//     * The default concurrency level for this table. Unused but
//     * defined for compatibility with previous versions of this class.
//     */
//    private static final int DEFAULT_CONCURRENCY_LEVEL = 16;
//
//    /**
//     * The load factor for this table. Overrides of this value in
//     * constructors affect only the initial table capacity.  The
//     * actual floating point value isn't normally used -- it is
//     * simpler to use expressions such as {@code n - (n >>> 2)} for
//     * the associated resizing threshold.
//     */
//    private static final float LOAD_FACTOR = 0.75f;
//
//    /**
//     * The bin count threshold for using a tree rather than list for a
//     * bin.  Bins are converted to trees when adding an element to a
//     * bin with at least this many nodes. The value must be greater
//     * than 2, and should be at least 8 to mesh with assumptions in
//     * tree removal about conversion back to plain bins upon
//     * shrinkage.
//     */
//    static final int TREEIFY_THRESHOLD = 8;
//
//    /**
//     * The bin count threshold for untreeifying a (split) bin during a
//     * resize operation. Should be less than TREEIFY_THRESHOLD, and at
//     * most 6 to mesh with shrinkage detection under removal.
//     */
//    static final int UNTREEIFY_THRESHOLD = 6;
//
//    /**
//     * The smallest table capacity for which bins may be treeified.
//     * (Otherwise the table is resized if too many nodes in a bin.)
//     * The value should be at least 4 * TREEIFY_THRESHOLD to avoid
//     * conflicts between resizing and treeification thresholds.
//     */
//    static final int MIN_TREEIFY_CAPACITY = 64;
//
//    /**
//     * Minimum number of rebinnings per transfer step. Ranges are
//     * subdivided to allow multiple resizer threads.  This value
//     * serves as a lower bound to avoid resizers encountering
//     * excessive memory contention.  The value should be at least
//     * DEFAULT_CAPACITY.
//     */
//    private static final int MIN_TRANSFER_STRIDE = 16;
//
//    /**
//     * The number of bits used for generation stamp in sizeCtl.
//     * Must be at least 6 for 32bit arrays.
//     */
//    private static int RESIZE_STAMP_BITS = 16;
//
//    /**
//     * The maximum number of threads that can help resize.
//     * Must fit in 32 - RESIZE_STAMP_BITS bits.
//     */
//    private static final int MAX_RESIZERS = (1 << (32 - RESIZE_STAMP_BITS)) - 1;
//
//    /**
//     * The bit shift for recording size stamp in sizeCtl.
//     */
//    private static final int RESIZE_STAMP_SHIFT = 32 - RESIZE_STAMP_BITS;
//
//    /*
//     * Encodings for Node hash fields. See above for explanation.
//     */
//    // ForwardingNode标记节点的hash值（表示正在扩容）
//    static final int MOVED     = -1; // hash for forwarding nodes
//    // TreeBin节点的hash值，它是对应桶的根节点
//    static final int TREEBIN   = -2; // hash for roots of trees
//    static final int RESERVED  = -3; // hash for transient reservations
//    static final int HASH_BITS = 0x7fffffff; // usable bits of normal node hash
//
//    /** Number of CPUS, to place bounds on some sizings */
//    static final int NCPU = Runtime.getRuntime().availableProcessors();
//
//    /** For serialization compatibility. */
//    private static final ObjectStreamField[] serialPersistentFields = {
//            new ObjectStreamField("segments", Segment[].class),
//            new ObjectStreamField("segmentMask", Integer.TYPE),
//            new ObjectStreamField("segmentShift", Integer.TYPE)
//    };
//
//    /* ---------------- Nodes -------------- */
//
//    /**
//     * Key-value entry.  This class is never exported out as a
//     * user-mutable Map.Entry (i.e., one supporting setValue; see
//     * MapEntry below), but can be used for read-only traversals used
//     * in bulk tasks.  Subclasses of Node with a negative hash field
//     * are special, and contain null keys and values (but are never
//     * exported).  Otherwise, keys and vals are never null.
//     */
//    static class Node<K,V> implements Map.Entry<K,V> {
//        final int hash;
//        final K key;
//        volatile V val;
//        volatile Node<K,V> next;
//
//        Node(int hash, K key, V val, Node<K,V> next) {
//            this.hash = hash;
//            this.key = key;
//            this.val = val;
//            this.next = next;
//        }
//
//        public final K getKey()       { return key; }
//        public final V getValue()     { return val; }
//        public final int hashCode()   { return key.hashCode() ^ val.hashCode(); }
//        public final String toString(){ return key + "=" + val; }
//        public final V setValue(V value) {
//            throw new UnsupportedOperationException();
//        }
//
//        public final boolean equals(Object o) {
//            Object k, v, u; Map.Entry<?,?> e;
//            return ((o instanceof Map.Entry) &&
//                    (k = (e = (Map.Entry<?,?>)o).getKey()) != null &&
//                    (v = e.getValue()) != null &&
//                    (k == key || k.equals(key)) &&
//                    (v == (u = val) || v.equals(u)));
//        }
//
//        /**
//         * Virtualized support for map.get(); overridden in subclasses.
//         */
//        Node<K,V> find(int h, Object k) {
//            Node<K,V> e = this;
//            if (k != null) {
//                do {
//                    K ek;
//                    if (e.hash == h &&
//                            ((ek = e.key) == k || (ek != null && k.equals(ek))))
//                        return e;
//                } while ((e = e.next) != null);
//            }
//            return null;
//        }
//    }
//
//    /* ---------------- Static utilities -------------- */
//
//    /**
//     * Spreads (XORs) higher bits of hash to lower and also forces top
//     * bit to 0. Because the table uses power-of-two masking, sets of
//     * hashes that vary only in bits above the current mask will
//     * always collide. (Among known examples are sets of Float keys
//     * holding consecutive whole numbers in small tables.)  So we
//     * apply a transform that spreads the impact of higher bits
//     * downward. There is a tradeoff between speed, utility, and
//     * quality of bit-spreading. Because many common sets of hashes
//     * are already reasonably distributed (so don't benefit from
//     * spreading), and because we use trees to handle large sets of
//     * collisions in bins, we just XOR some shifted bits in the
//     * cheapest possible way to reduce systematic lossage, as well as
//     * to incorporate impact of the highest bits that would otherwise
//     * never be used in index calculations because of table bounds.
//     */
//    static final int spread(int h) {
//        return (h ^ (h >>> 16)) & HASH_BITS;
//    }
//
//    /**
//     * Returns a power of two table size for the given desired capacity.
//     * See Hackers Delight, sec 3.2
//     */
//    private static final int tableSizeFor(int c) {
//        int n = c - 1;
//        n |= n >>> 1;
//        n |= n >>> 2;
//        n |= n >>> 4;
//        n |= n >>> 8;
//        n |= n >>> 16;
//        return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
//    }
//
//    /**
//     * Returns x's Class if it is of the form "class C implements
//     * Comparable<C>", else null.
//     */
//    static Class<?> comparableClassFor(Object x) {
//        if (x instanceof Comparable) {
//            Class<?> c; Type[] ts, as; Type t; ParameterizedType p;
//            if ((c = x.getClass()) == String.class) // bypass checks
//                return c;
//            if ((ts = c.getGenericInterfaces()) != null) {
//                for (int i = 0; i < ts.length; ++i) {
//                    if (((t = ts[i]) instanceof ParameterizedType) &&
//                            ((p = (ParameterizedType)t).getRawType() ==
//                                    Comparable.class) &&
//                            (as = p.getActualTypeArguments()) != null &&
//                            as.length == 1 && as[0] == c) // type arg is c
//                        return c;
//                }
//            }
//        }
//        return null;
//    }
//
//    /**
//     * Returns k.compareTo(x) if x matches kc (k's screened comparable
//     * class), else 0.
//     */
//    @SuppressWarnings({"rawtypes","unchecked"}) // for cast to Comparable
//    static int compareComparables(Class<?> kc, Object k, Object x) {
//        return (x == null || x.getClass() != kc ? 0 :
//                ((Comparable)k).compareTo(x));
//    }
//
//    /* ---------------- Table element access -------------- */
//
//    /*
//     * Volatile access methods are used for table elements as well as
//     * elements of in-progress next table while resizing.  All uses of
//     * the tab arguments must be null checked by callers.  All callers
//     * also paranoically precheck that tab's length is not zero (or an
//     * equivalent check), thus ensuring that any index argument taking
//     * the form of a hash value anded with (length - 1) is a valid
//     * index.  Note that, to be correct wrt arbitrary concurrency
//     * errors by users, these checks must operate on local variables,
//     * which accounts for some odd-looking inline assignments below.
//     * Note that calls to setTabAt always occur within locked regions,
//     * and so in principle require only release ordering, not
//     * full volatile semantics, but are currently coded as volatile
//     * writes to be conservative.
//     */
//
//    @SuppressWarnings("unchecked")
//    static final <K,V> Node<K,V> tabAt(Node<K,V>[] tab, int i) {
//        return (Node<K,V>)U.getObjectVolatile(tab, ((long)i << ASHIFT) + ABASE);
//    }
//
//    static final <K,V> boolean casTabAt(Node<K,V>[] tab, int i,
//                                        Node<K,V> c, Node<K,V> v) {
//        return U.compareAndSwapObject(tab, ((long)i << ASHIFT) + ABASE, c, v);
//    }
//
//    static final <K,V> void setTabAt(Node<K,V>[] tab, int i, Node<K,V> v) {
//        U.putObjectVolatile(tab, ((long)i << ASHIFT) + ABASE, v);
//    }
//
//    /* ---------------- Fields -------------- */
//
//    /**
//     * The array of bins. Lazily initialized upon first insertion.
//     * Size is always a power of two. Accessed directly by iterators.
//     */
//    transient volatile Node<K,V>[] table;
//
//    /**
//     * The next table to use; non-null only while resizing.
//     */
//    private transient volatile Node<K,V>[] nextTable;
//
//    /**
//     * Base counter value, used mainly when there is no contention,
//     * but also as a fallback during table initialization
//     * races. Updated via CAS.
//     */
//    // 基本计数器值，主要在没有争用时使用，但也作为表初始化比赛期间的后备。通过CAS更新。
//    private transient volatile long baseCount;
//
//    /**
//     * Table initialization and resizing control.  When negative, the
//     * table is being initialized or resized: -1 for initialization,
//     * else -(1 + the number of active resizing threads).  Otherwise,
//     * when table is null, holds the initial table size to use upon
//     * creation, or 0 for default. After initialization, holds the
//     * next element count value upon which to resize the table.
//     */
//    /**
//     * 控制table数组的初始化和扩容，不同的值有不同的含义：
//     * -1:表示正在初始化
//     * -n:表示有n-1个线程正在扩容
//     * 0:表示还未初始化，默认值
//     * 大于0：表示下一次扩容的阈值
//     */
//    private transient volatile int sizeCtl;
//
//    /**
//     * The next table index (plus one) to split while resizing.
//     */
//    private transient volatile int transferIndex;
//
//    /**
//     * Spinlock (locked via CAS) used when resizing and/or creating CounterCells.
//     */
//    private transient volatile int cellsBusy;
//
//    /**
//     * Table of counter cells. When non-null, size is a power of 2.
//     * 计数器表。当非null时，size是2的幂。
//     */
//    private transient volatile CounterCell[] counterCells;
//
//    // views
//    private transient KeySetView<K,V> keySet;
//    private transient ValuesView<K,V> values;
//    private transient EntrySetView<K,V> entrySet;
//
//
//    /* ---------------- Public operations -------------- */
//
//    /**
//     * Creates a new, empty map with the default initial table size (16).
//     */
//    public ConcurrentHashMap18() {
//    }
//
//    /**
//     * Creates a new, empty map with an initial table size
//     * accommodating the specified number of elements without the need
//     * to dynamically resize.
//     *
//     * @param initialCapacity The implementation performs internal
//     * sizing to accommodate this many elements.
//     * @throws IllegalArgumentException if the initial capacity of
//     * elements is negative
//     */
//    public ConcurrentHashMap18(int initialCapacity) {
//        if (initialCapacity < 0)
//            throw new IllegalArgumentException();
//        int cap = ((initialCapacity >= (MAXIMUM_CAPACITY >>> 1)) ?
//                MAXIMUM_CAPACITY :
//                tableSizeFor(initialCapacity + (initialCapacity >>> 1) + 1));
//        this.sizeCtl = cap;
//    }
//
//    /**
//     * Creates a new map with the same mappings as the given map.
//     *
//     * @param m the map
//     */
//    public ConcurrentHashMap18(Map<? extends K, ? extends V> m) {
//        this.sizeCtl = DEFAULT_CAPACITY;
//        putAll(m);
//    }
//
//    /**
//     * Creates a new, empty map with an initial table size based on
//     * the given number of elements ({@code initialCapacity}) and
//     * initial table density ({@code loadFactor}).
//     *
//     * @param initialCapacity the initial capacity. The implementation
//     * performs internal sizing to accommodate this many elements,
//     * given the specified load factor.
//     * @param loadFactor the load factor (table density) for
//     * establishing the initial table size
//     * @throws IllegalArgumentException if the initial capacity of
//     * elements is negative or the load factor is nonpositive
//     *
//     * @since 1.6
//     */
//    public ConcurrentHashMap18(int initialCapacity, float loadFactor) {
//        this(initialCapacity, loadFactor, 1);
//    }
//
//    /**
//     * Creates a new, empty map with an initial table size based on
//     * the given number of elements ({@code initialCapacity}), table
//     * density ({@code loadFactor}), and number of concurrently
//     * updating threads ({@code concurrencyLevel}).
//     *
//     * @param initialCapacity the initial capacity. The implementation
//     * performs internal sizing to accommodate this many elements,
//     * given the specified load factor.
//     * @param loadFactor the load factor (table density) for
//     * establishing the initial table size
//     * @param concurrencyLevel the estimated number of concurrently
//     * updating threads. The implementation may use this value as
//     * a sizing hint.
//     * @throws IllegalArgumentException if the initial capacity is
//     * negative or the load factor or concurrencyLevel are
//     * nonpositive
//     */
//    public ConcurrentHashMap18(int initialCapacity,
//                               float loadFactor, int concurrencyLevel) {
//        if (!(loadFactor > 0.0f) || initialCapacity < 0 || concurrencyLevel <= 0)
//            throw new IllegalArgumentException();
//        if (initialCapacity < concurrencyLevel)   // Use at least as many bins
//            initialCapacity = concurrencyLevel;   // as estimated threads
//        long size = (long)(1.0 + (long)initialCapacity / loadFactor);
//        int cap = (size >= (long)MAXIMUM_CAPACITY) ?
//                MAXIMUM_CAPACITY : tableSizeFor((int)size);
//        this.sizeCtl = cap;
//    }
//
//    // Original (since JDK1.2) Map methods
//
//    /**
//     * {@inheritDoc}
//     */
//    public int size() {
//        long n = sumCount();
//        return ((n < 0L) ? 0 :
//                (n > (long)Integer.MAX_VALUE) ? Integer.MAX_VALUE :
//                        (int)n);
//    }
//
//    /**
//     * {@inheritDoc}
//     */
//    public boolean isEmpty() {
//        return sumCount() <= 0L; // ignore transient negative values
//    }
//
//    /**
//     * Returns the value to which the specified key is mapped,
//     * or {@code null} if this map contains no mapping for the key.
//     *
//     * <p>More formally, if this map contains a mapping from a key
//     * {@code k} to a value {@code v} such that {@code key.equals(k)},
//     * then this method returns {@code v}; otherwise it returns
//     * {@code null}.  (There can be at most one such mapping.)
//     *
//     * @throws NullPointerException if the specified key is null
//     */
//    public V get(Object key) {
//        Node<K,V>[] tab; Node<K,V> e, p; int n, eh; K ek;
//        int h = spread(key.hashCode());
//        // table 不为NULL并且对饮索引位不为NULL
//        if ((tab = table) != null && (n = tab.length) > 0 &&
//                (e = tabAt(tab, (n - 1) & h)) != null) {
//            if ((eh = e.hash) == h) {
//                // 头节点key相同
//                if ((ek = e.key) == key || (ek != null && key.equals(ek)))
//                    return e.val;
//            }
//            // 树节点或者是ForwardingNode标记节点
//            else if (eh < 0)
//                return (p = e.find(h, key)) != null ? p.val : null;
//            // 链表节点
//            while ((e = e.next) != null) {
//                // key
//                if (e.hash == h &&
//                        ((ek = e.key) == key || (ek != null && key.equals(ek))))
//                    return e.val;
//            }
//        }
//        return null;
//    }
//
//    /**
//     * Tests if the specified object is a key in this table.
//     *
//     * @param  key possible key
//     * @return {@code true} if and only if the specified object
//     *         is a key in this table, as determined by the
//     *         {@code equals} method; {@code false} otherwise
//     * @throws NullPointerException if the specified key is null
//     */
//    public boolean containsKey(Object key) {
//        return get(key) != null;
//    }
//
//    /**
//     * Returns {@code true} if this map maps one or more keys to the
//     * specified value. Note: This method may require a full traversal
//     * of the map, and is much slower than method {@code containsKey}.
//     *
//     * @param value value whose presence in this map is to be tested
//     * @return {@code true} if this map maps one or more keys to the
//     *         specified value
//     * @throws NullPointerException if the specified value is null
//     */
//    public boolean containsValue(Object value) {
//        if (value == null)
//            throw new NullPointerException();
//        Node<K,V>[] t;
//        if ((t = table) != null) {
//            Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
//            for (Node<K,V> p; (p = it.advance()) != null; ) {
//                V v;
//                if ((v = p.val) == value || (v != null && value.equals(v)))
//                    return true;
//            }
//        }
//        return false;
//    }
//
//    /**
//     * Maps the specified key to the specified value in this table.
//     * Neither the key nor the value can be null.
//     *
//     * <p>The value can be retrieved by calling the {@code get} method
//     * with a key that is equal to the original key.
//     *
//     * @param key key with which the specified value is to be associated
//     * @param value value to be associated with the specified key
//     * @return the previous value associated with {@code key}, or
//     *         {@code null} if there was no mapping for {@code key}
//     * @throws NullPointerException if the specified key or value is null
//     */
//    public V put(K key, V value) {
//        return putVal(key, value, false);
//    }
//
//    /** Implementation for put and putIfAbsent */
//    final V putVal(K key, V value, boolean onlyIfAbsent) {
//        if (key == null || value == null) throw new NullPointerException();
//        // 计算hash值
//        int hash = spread(key.hashCode());
//        int binCount = 0;
//        for (Node<K,V>[] tab = table;;) {
//            Node<K,V> f; int n, i, fh;
//            // 判断是否需要初始化
//            if (tab == null || (n = tab.length) == 0)
//                tab = initTable();
//                // 找出key对应的索引位上的第一个节点
//            else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
//                // 如果该索引位为null，则直接将数据放到该索引位
//                if (casTabAt(tab, i, null,
//                        new Node<K,V>(hash, key, value, null)))
//                    break;                   // no lock when adding to empty bin
//            }
//            // 正在扩容
//            else if ((fh = f.hash) == MOVED)
//                tab = helpTransfer(tab, f);
//            else {
//                V oldVal = null;
//                // 加内置锁锁定一个数组的索引位，并添加节点
//                synchronized (f) {
//                    if (tabAt(tab, i) == f) {
//                        // 表示链表节点
//                        if (fh >= 0) {
//                            binCount = 1;
//                            for (Node<K,V> e = f;; ++binCount) {
//                                K ek;
//                                // key相同直接替换value值
//                                if (e.hash == hash &&
//                                        ((ek = e.key) == key ||
//                                                (ek != null && key.equals(ek)))) {
//                                    oldVal = e.val;
//                                    if (!onlyIfAbsent)
//                                        e.val = value;
//                                    break;
//                                }
//                                // 将新节点添加到链表尾部
//                                Node<K,V> pred = e;
//                                if ((e = e.next) == null) {
//                                    pred.next = new Node<K,V>(hash, key,
//                                            value, null);
//                                    break;
//                                }
//                            }
//                        }
//                        // 表示树节点
//                        else if (f instanceof TreeBin) {
//                            Node<K,V> p;
//                            binCount = 2;
//                            // 添加数节点
//                            if ((p = ((TreeBin<K,V>)f).putTreeVal(hash, key,
//                                    value)) != null) {
//                                oldVal = p.val;
//                                if (!onlyIfAbsent)
//                                    p.val = value;
//                            }
//                        }
//                    }
//                }
//                if (binCount != 0) {
//                    // 尝试将链表转换成红黑树
//                    if (binCount >= TREEIFY_THRESHOLD)
//                        treeifyBin(tab, i);
//                    if (oldVal != null)
//                        return oldVal;
//                    break;
//                }
//            }
//        }
//        addCount(1L, binCount);
//        return null;
//    }
//
//    /**
//     * Copies all of the mappings from the specified map to this one.
//     * These mappings replace any mappings that this map had for any of the
//     * keys currently in the specified map.
//     *
//     * @param m mappings to be stored in this map
//     */
//    public void putAll(Map<? extends K, ? extends V> m) {
//        tryPresize(m.size());
//        for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
//            putVal(e.getKey(), e.getValue(), false);
//    }
//
//    /**
//     * Removes the key (and its corresponding value) from this map.
//     * This method does nothing if the key is not in the map.
//     *
//     * @param  key the key that needs to be removed
//     * @return the previous value associated with {@code key}, or
//     *         {@code null} if there was no mapping for {@code key}
//     * @throws NullPointerException if the specified key is null
//     */
//    public V remove(Object key) {
//        return replaceNode(key, null, null);
//    }
//
//    /**
//     * Implementation for the four public remove/replace methods:
//     * Replaces node value with v, conditional upon match of cv if
//     * non-null.  If resulting value is null, delete.
//     */
//    final V replaceNode(Object key, V value, Object cv) {
//        int hash = spread(key.hashCode());
//        for (Node<K,V>[] tab = table;;) {
//            Node<K,V> f; int n, i, fh;
//            if (tab == null || (n = tab.length) == 0 ||
//                    (f = tabAt(tab, i = (n - 1) & hash)) == null)
//                break;
//            else if ((fh = f.hash) == MOVED)
//                tab = helpTransfer(tab, f);
//            else {
//                V oldVal = null;
//                boolean validated = false;
//                synchronized (f) {
//                    if (tabAt(tab, i) == f) {
//                        if (fh >= 0) {
//                            validated = true;
//                            for (Node<K,V> e = f, pred = null;;) {
//                                K ek;
//                                if (e.hash == hash &&
//                                        ((ek = e.key) == key ||
//                                                (ek != null && key.equals(ek)))) {
//                                    V ev = e.val;
//                                    if (cv == null || cv == ev ||
//                                            (ev != null && cv.equals(ev))) {
//                                        oldVal = ev;
//                                        if (value != null)
//                                            e.val = value;
//                                        else if (pred != null)
//                                            pred.next = e.next;
//                                        else
//                                            setTabAt(tab, i, e.next);
//                                    }
//                                    break;
//                                }
//                                pred = e;
//                                if ((e = e.next) == null)
//                                    break;
//                            }
//                        }
//                        else if (f instanceof TreeBin) {
//                            validated = true;
//                            TreeBin<K,V> t = (TreeBin<K,V>)f;
//                            TreeNode<K,V> r, p;
//                            if ((r = t.root) != null &&
//                                    (p = r.findTreeNode(hash, key, null)) != null) {
//                                V pv = p.val;
//                                if (cv == null || cv == pv ||
//                                        (pv != null && cv.equals(pv))) {
//                                    oldVal = pv;
//                                    if (value != null)
//                                        p.val = value;
//                                    else if (t.removeTreeNode(p))
//                                        setTabAt(tab, i, untreeify(t.first));
//                                }
//                            }
//                        }
//                    }
//                }
//                if (validated) {
//                    if (oldVal != null) {
//                        if (value == null)
//                            addCount(-1L, -1);
//                        return oldVal;
//                    }
//                    break;
//                }
//            }
//        }
//        return null;
//    }
//
//    /**
//     * Removes all of the mappings from this map.
//     */
//    public void clear() {
//        long delta = 0L; // negative number of deletions
//        int i = 0;
//        Node<K,V>[] tab = table;
//        while (tab != null && i < tab.length) {
//            int fh;
//            Node<K,V> f = tabAt(tab, i);
//            if (f == null)
//                ++i;
//            else if ((fh = f.hash) == MOVED) {
//                tab = helpTransfer(tab, f);
//                i = 0; // restart
//            }
//            else {
//                synchronized (f) {
//                    if (tabAt(tab, i) == f) {
//                        Node<K,V> p = (fh >= 0 ? f :
//                                (f instanceof TreeBin) ?
//                                        ((TreeBin<K,V>)f).first : null);
//                        while (p != null) {
//                            --delta;
//                            p = p.next;
//                        }
//                        setTabAt(tab, i++, null);
//                    }
//                }
//            }
//        }
//        if (delta != 0L)
//            addCount(delta, -1);
//    }
//
//    /**
//     * Returns a {@link Set} view of the keys contained in this map.
//     * The set is backed by the map, so changes to the map are
//     * reflected in the set, and vice-versa. The set supports element
//     * removal, which removes the corresponding mapping from this map,
//     * via the {@code Iterator.remove}, {@code Set.remove},
//     * {@code removeAll}, {@code retainAll}, and {@code clear}
//     * operations.  It does not support the {@code add} or
//     * {@code addAll} operations.
//     *
//     * <p>The view's iterators and spliterators are
//     * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
//     *
//     * <p>The view's {@code spliterator} reports {@link Spliterator#CONCURRENT},
//     * {@link Spliterator#DISTINCT}, and {@link Spliterator#NONNULL}.
//     *
//     * @return the set view
//     */
//    public KeySetView<K,V> keySet() {
//        KeySetView<K,V> ks;
//        return (ks = keySet) != null ? ks : (keySet = new KeySetView<K,V>(this, null));
//    }
//
//    /**
//     * Returns a {@link Collection} view of the values contained in this map.
//     * The collection is backed by the map, so changes to the map are
//     * reflected in the collection, and vice-versa.  The collection
//     * supports element removal, which removes the corresponding
//     * mapping from this map, via the {@code Iterator.remove},
//     * {@code Collection.remove}, {@code removeAll},
//     * {@code retainAll}, and {@code clear} operations.  It does not
//     * support the {@code add} or {@code addAll} operations.
//     *
//     * <p>The view's iterators and spliterators are
//     * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
//     *
//     * <p>The view's {@code spliterator} reports {@link Spliterator#CONCURRENT}
//     * and {@link Spliterator#NONNULL}.
//     *
//     * @return the collection view
//     */
//    public Collection<V> values() {
//        ValuesView<K,V> vs;
//        return (vs = values) != null ? vs : (values = new ValuesView<K,V>(this));
//    }
//
//    /**
//     * Returns a {@link Set} view of the mappings contained in this map.
//     * The set is backed by the map, so changes to the map are
//     * reflected in the set, and vice-versa.  The set supports element
//     * removal, which removes the corresponding mapping from the map,
//     * via the {@code Iterator.remove}, {@code Set.remove},
//     * {@code removeAll}, {@code retainAll}, and {@code clear}
//     * operations.
//     *
//     * <p>The view's iterators and spliterators are
//     * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
//     *
//     * <p>The view's {@code spliterator} reports {@link Spliterator#CONCURRENT},
//     * {@link Spliterator#DISTINCT}, and {@link Spliterator#NONNULL}.
//     *
//     * @return the set view
//     */
//    public Set<Map.Entry<K,V>> entrySet() {
//        EntrySetView<K,V> es;
//        return (es = entrySet) != null ? es : (entrySet = new EntrySetView<K,V>(this));
//    }
//
//    /**
//     * Returns the hash code value for this {@link Map}, i.e.,
//     * the sum of, for each key-value pair in the map,
//     * {@code key.hashCode() ^ value.hashCode()}.
//     *
//     * @return the hash code value for this map
//     */
//    public int hashCode() {
//        int h = 0;
//        Node<K,V>[] t;
//        if ((t = table) != null) {
//            Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
//            for (Node<K,V> p; (p = it.advance()) != null; )
//                h += p.key.hashCode() ^ p.val.hashCode();
//        }
//        return h;
//    }
//
//    /**
//     * Returns a string representation of this map.  The string
//     * representation consists of a list of key-value mappings (in no
//     * particular order) enclosed in braces ("{@code {}}").  Adjacent
//     * mappings are separated by the characters {@code ", "} (comma
//     * and space).  Each key-value mapping is rendered as the key
//     * followed by an equals sign ("{@code =}") followed by the
//     * associated value.
//     *
//     * @return a string representation of this map
//     */
//    public String toString() {
//        Node<K,V>[] t;
//        int f = (t = table) == null ? 0 : t.length;
//        Traverser<K,V> it = new Traverser<K,V>(t, f, 0, f);
//        StringBuilder sb = new StringBuilder();
//        sb.append('{');
//        Node<K,V> p;
//        if ((p = it.advance()) != null) {
//            for (;;) {
//                K k = p.key;
//                V v = p.val;
//                sb.append(k == this ? "(this Map)" : k);
//                sb.append('=');
//                sb.append(v == this ? "(this Map)" : v);
//                if ((p = it.advance()) == null)
//                    break;
//                sb.append(',').append(' ');
//            }
//        }
//        return sb.append('}').toString();
//    }
//
//    /**
//     * Compares the specified object with this map for equality.
//     * Returns {@code true} if the given object is a map with the same
//     * mappings as this map.  This operation may return misleading
//     * results if either map is concurrently modified during execution
//     * of this method.
//     *
//     * @param o object to be compared for equality with this map
//     * @return {@code true} if the specified object is equal to this map
//     */
//    public boolean equals(Object o) {
//        if (o != this) {
//            if (!(o instanceof Map))
//                return false;
//            Map<?,?> m = (Map<?,?>) o;
//            Node<K,V>[] t;
//            int f = (t = table) == null ? 0 : t.length;
//            Traverser<K,V> it = new Traverser<K,V>(t, f, 0, f);
//            for (Node<K,V> p; (p = it.advance()) != null; ) {
//                V val = p.val;
//                Object v = m.get(p.key);
//                if (v == null || (v != val && !v.equals(val)))
//                    return false;
//            }
//            for (Map.Entry<?,?> e : m.entrySet()) {
//                Object mk, mv, v;
//                if ((mk = e.getKey()) == null ||
//                        (mv = e.getValue()) == null ||
//                        (v = get(mk)) == null ||
//                        (mv != v && !mv.equals(v)))
//                    return false;
//            }
//        }
//        return true;
//    }
//
//    /**
//     * Stripped-down version of helper class used in previous version,
//     * declared for the sake of serialization compatibility
//     */
//    static class Segment<K,V> extends ReentrantLock implements Serializable {
//        private static final long serialVersionUID = 2249069246763182397L;
//        final float loadFactor;
//        Segment(float lf) { this.loadFactor = lf; }
//    }
//
//    /**
//     * Saves the state of the {@code ConcurrentHashMap} instance to a
//     * stream (i.e., serializes it).
//     * @param s the stream
//     * @throws java.io.IOException if an I/O error occurs
//     * @serialData
//     * the key (Object) and value (Object)
//     * for each key-value mapping, followed by a null pair.
//     * The key-value mappings are emitted in no particular order.
//     */
//    private void writeObject(java.io.ObjectOutputStream s)
//            throws java.io.IOException {
//        // For serialization compatibility
//        // Emulate segment calculation from previous version of this class
//        int sshift = 0;
//        int ssize = 1;
//        while (ssize < DEFAULT_CONCURRENCY_LEVEL) {
//            ++sshift;
//            ssize <<= 1;
//        }
//        int segmentShift = 32 - sshift;
//        int segmentMask = ssize - 1;
//        @SuppressWarnings("unchecked")
//        Segment<K,V>[] segments = (Segment<K,V>[])
//                new Segment<?,?>[DEFAULT_CONCURRENCY_LEVEL];
//        for (int i = 0; i < segments.length; ++i)
//            segments[i] = new Segment<K,V>(LOAD_FACTOR);
//        s.putFields().put("segments", segments);
//        s.putFields().put("segmentShift", segmentShift);
//        s.putFields().put("segmentMask", segmentMask);
//        s.writeFields();
//
//        Node<K,V>[] t;
//        if ((t = table) != null) {
//            Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
//            for (Node<K,V> p; (p = it.advance()) != null; ) {
//                s.writeObject(p.key);
//                s.writeObject(p.val);
//            }
//        }
//        s.writeObject(null);
//        s.writeObject(null);
//        segments = null; // throw away
//    }
//
//    /**
//     * Reconstitutes the instance from a stream (that is, deserializes it).
//     * @param s the stream
//     * @throws ClassNotFoundException if the class of a serialized object
//     *         could not be found
//     * @throws java.io.IOException if an I/O error occurs
//     */
//    private void readObject(java.io.ObjectInputStream s)
//            throws java.io.IOException, ClassNotFoundException {
//        /*
//         * To improve performance in typical cases, we create nodes
//         * while reading, then place in table once size is known.
//         * However, we must also validate uniqueness and deal with
//         * overpopulated bins while doing so, which requires
//         * specialized versions of putVal mechanics.
//         */
//        sizeCtl = -1; // force exclusion for table construction
//        s.defaultReadObject();
//        long size = 0L;
//        Node<K,V> p = null;
//        for (;;) {
//            @SuppressWarnings("unchecked")
//            K k = (K) s.readObject();
//            @SuppressWarnings("unchecked")
//            V v = (V) s.readObject();
//            if (k != null && v != null) {
//                p = new Node<K,V>(spread(k.hashCode()), k, v, p);
//                ++size;
//            }
//            else
//                break;
//        }
//        if (size == 0L)
//            sizeCtl = 0;
//        else {
//            int n;
//            if (size >= (long)(MAXIMUM_CAPACITY >>> 1))
//                n = MAXIMUM_CAPACITY;
//            else {
//                int sz = (int)size;
//                n = tableSizeFor(sz + (sz >>> 1) + 1);
//            }
//            @SuppressWarnings("unchecked")
//            Node<K,V>[] tab = (Node<K,V>[])new Node<?,?>[n];
//            int mask = n - 1;
//            long added = 0L;
//            while (p != null) {
//                boolean insertAtFront;
//                Node<K,V> next = p.next, first;
//                int h = p.hash, j = h & mask;
//                if ((first = tabAt(tab, j)) == null)
//                    insertAtFront = true;
//                else {
//                    K k = p.key;
//                    if (first.hash < 0) {
//                        TreeBin<K,V> t = (TreeBin<K,V>)first;
//                        if (t.putTreeVal(h, k, p.val) == null)
//                            ++added;
//                        insertAtFront = false;
//                    }
//                    else {
//                        int binCount = 0;
//                        insertAtFront = true;
//                        Node<K,V> q; K qk;
//                        for (q = first; q != null; q = q.next) {
//                            if (q.hash == h &&
//                                    ((qk = q.key) == k ||
//                                            (qk != null && k.equals(qk)))) {
//                                insertAtFront = false;
//                                break;
//                            }
//                            ++binCount;
//                        }
//                        if (insertAtFront && binCount >= TREEIFY_THRESHOLD) {
//                            insertAtFront = false;
//                            ++added;
//                            p.next = first;
//                            TreeNode<K,V> hd = null, tl = null;
//                            for (q = p; q != null; q = q.next) {
//                                TreeNode<K,V> t = new TreeNode<K,V>
//                                        (q.hash, q.key, q.val, null, null);
//                                if ((t.prev = tl) == null)
//                                    hd = t;
//                                else
//                                    tl.next = t;
//                                tl = t;
//                            }
//                            setTabAt(tab, j, new TreeBin<K,V>(hd));
//                        }
//                    }
//                }
//                if (insertAtFront) {
//                    ++added;
//                    p.next = first;
//                    setTabAt(tab, j, p);
//                }
//                p = next;
//            }
//            table = tab;
//            sizeCtl = n - (n >>> 2);
//            baseCount = added;
//        }
//    }
//
//    // ConcurrentMap methods
//
//    /**
//     * {@inheritDoc}
//     *
//     * @return the previous value associated with the specified key,
//     *         or {@code null} if there was no mapping for the key
//     * @throws NullPointerException if the specified key or value is null
//     */
//    public V putIfAbsent(K key, V value) {
//        return putVal(key, value, true);
//    }
//
//    /**
//     * {@inheritDoc}
//     *
//     * @throws NullPointerException if the specified key is null
//     */
//    public boolean remove(Object key, Object value) {
//        if (key == null)
//            throw new NullPointerException();
//        return value != null && replaceNode(key, null, value) != null;
//    }
//
//    /**
//     * {@inheritDoc}
//     *
//     * @throws NullPointerException if any of the arguments are null
//     */
//    public boolean replace(K key, V oldValue, V newValue) {
//        if (key == null || oldValue == null || newValue == null)
//            throw new NullPointerException();
//        return replaceNode(key, newValue, oldValue) != null;
//    }
//
//    /**
//     * {@inheritDoc}
//     *
//     * @return the previous value associated with the specified key,
//     *         or {@code null} if there was no mapping for the key
//     * @throws NullPointerException if the specified key or value is null
//     */
//    public V replace(K key, V value) {
//        if (key == null || value == null)
//            throw new NullPointerException();
//        return replaceNode(key, value, null);
//    }
//
//    // Overrides of JDK8+ Map extension method defaults
//
//    /**
//     * Returns the value to which the specified key is mapped, or the
//     * given default value if this map contains no mapping for the
//     * key.
//     *
//     * @param key the key whose associated value is to be returned
//     * @param defaultValue the value to return if this map contains
//     * no mapping for the given key
//     * @return the mapping for the key, if present; else the default value
//     * @throws NullPointerException if the specified key is null
//     */
//    public V getOrDefault(Object key, V defaultValue) {
//        V v;
//        return (v = get(key)) == null ? defaultValue : v;
//    }
//
//    public void forEach(BiConsumer<? super K, ? super V> action) {
//        if (action == null) throw new NullPointerException();
//        Node<K,V>[] t;
//        if ((t = table) != null) {
//            Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
//            for (Node<K,V> p; (p = it.advance()) != null; ) {
//                action.accept(p.key, p.val);
//            }
//        }
//    }
//
//    public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
//        if (function == null) throw new NullPointerException();
//        Node<K,V>[] t;
//        if ((t = table) != null) {
//            Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
//            for (Node<K,V> p; (p = it.advance()) != null; ) {
//                V oldValue = p.val;
//                for (K key = p.key;;) {
//                    V newValue = function.apply(key, oldValue);
//                    if (newValue == null)
//                        throw new NullPointerException();
//                    if (replaceNode(key, newValue, oldValue) != null ||
//                            (oldValue = get(key)) == null)
//                        break;
//                }
//            }
//        }
//    }
//
//    /**
//     * If the specified key is not already associated with a value,
//     * attempts to compute its value using the given mapping function
//     * and enters it into this map unless {@code null}.  The entire
//     * method invocation is performed atomically, so the function is
//     * applied at most once per key.  Some attempted update operations
//     * on this map by other threads may be blocked while computation
//     * is in progress, so the computation should be short and simple,
//     * and must not attempt to update any other mappings of this map.
//     *
//     * @param key key with which the specified value is to be associated
//     * @param mappingFunction the function to compute a value
//     * @return the current (existing or computed) value associated with
//     *         the specified key, or null if the computed value is null
//     * @throws NullPointerException if the specified key or mappingFunction
//     *         is null
//     * @throws IllegalStateException if the computation detectably
//     *         attempts a recursive update to this map that would
//     *         otherwise never complete
//     * @throws RuntimeException or Error if the mappingFunction does so,
//     *         in which case the mapping is left unestablished
//     */
//    public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
//        if (key == null || mappingFunction == null)
//            throw new NullPointerException();
//        int h = spread(key.hashCode());
//        V val = null;
//        int binCount = 0;
//        for (Node<K,V>[] tab = table;;) {
//            Node<K,V> f; int n, i, fh;
//            if (tab == null || (n = tab.length) == 0)
//                tab = initTable();
//            else if ((f = tabAt(tab, i = (n - 1) & h)) == null) {
//                Node<K,V> r = new ReservationNode<K,V>();
//                synchronized (r) {
//                    if (casTabAt(tab, i, null, r)) {
//                        binCount = 1;
//                        Node<K,V> node = null;
//                        try {
//                            if ((val = mappingFunction.apply(key)) != null)
//                                node = new Node<K,V>(h, key, val, null);
//                        } finally {
//                            setTabAt(tab, i, node);
//                        }
//                    }
//                }
//                if (binCount != 0)
//                    break;
//            }
//            else if ((fh = f.hash) == MOVED)
//                tab = helpTransfer(tab, f);
//            else {
//                boolean added = false;
//                synchronized (f) {
//                    if (tabAt(tab, i) == f) {
//                        if (fh >= 0) {
//                            binCount = 1;
//                            for (Node<K,V> e = f;; ++binCount) {
//                                K ek; V ev;
//                                if (e.hash == h &&
//                                        ((ek = e.key) == key ||
//                                                (ek != null && key.equals(ek)))) {
//                                    val = e.val;
//                                    break;
//                                }
//                                Node<K,V> pred = e;
//                                if ((e = e.next) == null) {
//                                    if ((val = mappingFunction.apply(key)) != null) {
//                                        added = true;
//                                        pred.next = new Node<K,V>(h, key, val, null);
//                                    }
//                                    break;
//                                }
//                            }
//                        }
//                        else if (f instanceof TreeBin) {
//                            binCount = 2;
//                            TreeBin<K,V> t = (TreeBin<K,V>)f;
//                            TreeNode<K,V> r, p;
//                            if ((r = t.root) != null &&
//                                    (p = r.findTreeNode(h, key, null)) != null)
//                                val = p.val;
//                            else if ((val = mappingFunction.apply(key)) != null) {
//                                added = true;
//                                t.putTreeVal(h, key, val);
//                            }
//                        }
//                    }
//                }
//                if (binCount != 0) {
//                    if (binCount >= TREEIFY_THRESHOLD)
//                        treeifyBin(tab, i);
//                    if (!added)
//                        return val;
//                    break;
//                }
//            }
//        }
//        if (val != null)
//            addCount(1L, binCount);
//        return val;
//    }
//
//    /**
//     * If the value for the specified key is present, attempts to
//     * compute a new mapping given the key and its current mapped
//     * value.  The entire method invocation is performed atomically.
//     * Some attempted update operations on this map by other threads
//     * may be blocked while computation is in progress, so the
//     * computation should be short and simple, and must not attempt to
//     * update any other mappings of this map.
//     *
//     * @param key key with which a value may be associated
//     * @param remappingFunction the function to compute a value
//     * @return the new value associated with the specified key, or null if none
//     * @throws NullPointerException if the specified key or remappingFunction
//     *         is null
//     * @throws IllegalStateException if the computation detectably
//     *         attempts a recursive update to this map that would
//     *         otherwise never complete
//     * @throws RuntimeException or Error if the remappingFunction does so,
//     *         in which case the mapping is unchanged
//     */
//    public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
//        if (key == null || remappingFunction == null)
//            throw new NullPointerException();
//        int h = spread(key.hashCode());
//        V val = null;
//        int delta = 0;
//        int binCount = 0;
//        for (Node<K,V>[] tab = table;;) {
//            Node<K,V> f; int n, i, fh;
//            if (tab == null || (n = tab.length) == 0)
//                tab = initTable();
//            else if ((f = tabAt(tab, i = (n - 1) & h)) == null)
//                break;
//            else if ((fh = f.hash) == MOVED)
//                tab = helpTransfer(tab, f);
//            else {
//                synchronized (f) {
//                    if (tabAt(tab, i) == f) {
//                        if (fh >= 0) {
//                            binCount = 1;
//                            for (Node<K,V> e = f, pred = null;; ++binCount) {
//                                K ek;
//                                if (e.hash == h &&
//                                        ((ek = e.key) == key ||
//                                                (ek != null && key.equals(ek)))) {
//                                    val = remappingFunction.apply(key, e.val);
//                                    if (val != null)
//                                        e.val = val;
//                                    else {
//                                        delta = -1;
//                                        Node<K,V> en = e.next;
//                                        if (pred != null)
//                                            pred.next = en;
//                                        else
//                                            setTabAt(tab, i, en);
//                                    }
//                                    break;
//                                }
//                                pred = e;
//                                if ((e = e.next) == null)
//                                    break;
//                            }
//                        }
//                        else if (f instanceof TreeBin) {
//                            binCount = 2;
//                            TreeBin<K,V> t = (TreeBin<K,V>)f;
//                            TreeNode<K,V> r, p;
//                            if ((r = t.root) != null &&
//                                    (p = r.findTreeNode(h, key, null)) != null) {
//                                val = remappingFunction.apply(key, p.val);
//                                if (val != null)
//                                    p.val = val;
//                                else {
//                                    delta = -1;
//                                    if (t.removeTreeNode(p))
//                                        setTabAt(tab, i, untreeify(t.first));
//                                }
//                            }
//                        }
//                    }
//                }
//                if (binCount != 0)
//                    break;
//            }
//        }
//        if (delta != 0)
//            addCount((long)delta, binCount);
//        return val;
//    }
//
//    /**
//     * Attempts to compute a mapping for the specified key and its
//     * current mapped value (or {@code null} if there is no current
//     * mapping). The entire method invocation is performed atomically.
//     * Some attempted update operations on this map by other threads
//     * may be blocked while computation is in progress, so the
//     * computation should be short and simple, and must not attempt to
//     * update any other mappings of this Map.
//     *
//     * @param key key with which the specified value is to be associated
//     * @param remappingFunction the function to compute a value
//     * @return the new value associated with the specified key, or null if none
//     * @throws NullPointerException if the specified key or remappingFunction
//     *         is null
//     * @throws IllegalStateException if the computation detectably
//     *         attempts a recursive update to this map that would
//     *         otherwise never complete
//     * @throws RuntimeException or Error if the remappingFunction does so,
//     *         in which case the mapping is unchanged
//     */
//    public V compute(K key,
//                     BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
//        if (key == null || remappingFunction == null)
//            throw new NullPointerException();
//        int h = spread(key.hashCode());
//        V val = null;
//        int delta = 0;
//        int binCount = 0;
//        for (Node<K,V>[] tab = table;;) {
//            Node<K,V> f; int n, i, fh;
//            if (tab == null || (n = tab.length) == 0)
//                tab = initTable();
//            else if ((f = tabAt(tab, i = (n - 1) & h)) == null) {
//                Node<K,V> r = new ReservationNode<K,V>();
//                synchronized (r) {
//                    if (casTabAt(tab, i, null, r)) {
//                        binCount = 1;
//                        Node<K,V> node = null;
//                        try {
//                            if ((val = remappingFunction.apply(key, null)) != null) {
//                                delta = 1;
//                                node = new Node<K,V>(h, key, val, null);
//                            }
//                        } finally {
//                            setTabAt(tab, i, node);
//                        }
//                    }
//                }
//                if (binCount != 0)
//                    break;
//            }
//            else if ((fh = f.hash) == MOVED)
//                tab = helpTransfer(tab, f);
//            else {
//                synchronized (f) {
//                    if (tabAt(tab, i) == f) {
//                        if (fh >= 0) {
//                            binCount = 1;
//                            for (Node<K,V> e = f, pred = null;; ++binCount) {
//                                K ek;
//                                if (e.hash == h &&
//                                        ((ek = e.key) == key ||
//                                                (ek != null && key.equals(ek)))) {
//                                    val = remappingFunction.apply(key, e.val);
//                                    if (val != null)
//                                        e.val = val;
//                                    else {
//                                        delta = -1;
//                                        Node<K,V> en = e.next;
//                                        if (pred != null)
//                                            pred.next = en;
//                                        else
//                                            setTabAt(tab, i, en);
//                                    }
//                                    break;
//                                }
//                                pred = e;
//                                if ((e = e.next) == null) {
//                                    val = remappingFunction.apply(key, null);
//                                    if (val != null) {
//                                        delta = 1;
//                                        pred.next =
//                                                new Node<K,V>(h, key, val, null);
//                                    }
//                                    break;
//                                }
//                            }
//                        }
//                        else if (f instanceof TreeBin) {
//                            binCount = 1;
//                            TreeBin<K,V> t = (TreeBin<K,V>)f;
//                            TreeNode<K,V> r, p;
//                            if ((r = t.root) != null)
//                                p = r.findTreeNode(h, key, null);
//                            else
//                                p = null;
//                            V pv = (p == null) ? null : p.val;
//                            val = remappingFunction.apply(key, pv);
//                            if (val != null) {
//                                if (p != null)
//                                    p.val = val;
//                                else {
//                                    delta = 1;
//                                    t.putTreeVal(h, key, val);
//                                }
//                            }
//                            else if (p != null) {
//                                delta = -1;
//                                if (t.removeTreeNode(p))
//                                    setTabAt(tab, i, untreeify(t.first));
//                            }
//                        }
//                    }
//                }
//                if (binCount != 0) {
//                    if (binCount >= TREEIFY_THRESHOLD)
//                        treeifyBin(tab, i);
//                    break;
//                }
//            }
//        }
//        if (delta != 0)
//            addCount((long)delta, binCount);
//        return val;
//    }
//
//    /**
//     * If the specified key is not already associated with a
//     * (non-null) value, associates it with the given value.
//     * Otherwise, replaces the value with the results of the given
//     * remapping function, or removes if {@code null}. The entire
//     * method invocation is performed atomically.  Some attempted
//     * update operations on this map by other threads may be blocked
//     * while computation is in progress, so the computation should be
//     * short and simple, and must not attempt to update any other
//     * mappings of this Map.
//     *
//     * @param key key with which the specified value is to be associated
//     * @param value the value to use if absent
//     * @param remappingFunction the function to recompute a value if present
//     * @return the new value associated with the specified key, or null if none
//     * @throws NullPointerException if the specified key or the
//     *         remappingFunction is null
//     * @throws RuntimeException or Error if the remappingFunction does so,
//     *         in which case the mapping is unchanged
//     */
//    public V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
//        if (key == null || value == null || remappingFunction == null)
//            throw new NullPointerException();
//        int h = spread(key.hashCode());
//        V val = null;
//        int delta = 0;
//        int binCount = 0;
//        for (Node<K,V>[] tab = table;;) {
//            Node<K,V> f; int n, i, fh;
//            if (tab == null || (n = tab.length) == 0)
//                tab = initTable();
//            else if ((f = tabAt(tab, i = (n - 1) & h)) == null) {
//                if (casTabAt(tab, i, null, new Node<K,V>(h, key, value, null))) {
//                    delta = 1;
//                    val = value;
//                    break;
//                }
//            }
//            else if ((fh = f.hash) == MOVED)
//                tab = helpTransfer(tab, f);
//            else {
//                synchronized (f) {
//                    if (tabAt(tab, i) == f) {
//                        if (fh >= 0) {
//                            binCount = 1;
//                            for (Node<K,V> e = f, pred = null;; ++binCount) {
//                                K ek;
//                                if (e.hash == h &&
//                                        ((ek = e.key) == key ||
//                                                (ek != null && key.equals(ek)))) {
//                                    val = remappingFunction.apply(e.val, value);
//                                    if (val != null)
//                                        e.val = val;
//                                    else {
//                                        delta = -1;
//                                        Node<K,V> en = e.next;
//                                        if (pred != null)
//                                            pred.next = en;
//                                        else
//                                            setTabAt(tab, i, en);
//                                    }
//                                    break;
//                                }
//                                pred = e;
//                                if ((e = e.next) == null) {
//                                    delta = 1;
//                                    val = value;
//                                    pred.next =
//                                            new Node<K,V>(h, key, val, null);
//                                    break;
//                                }
//                            }
//                        }
//                        else if (f instanceof TreeBin) {
//                            binCount = 2;
//                            TreeBin<K,V> t = (TreeBin<K,V>)f;
//                            TreeNode<K,V> r = t.root;
//                            TreeNode<K,V> p = (r == null) ? null :
//                                    r.findTreeNode(h, key, null);
//                            val = (p == null) ? value :
//                                    remappingFunction.apply(p.val, value);
//                            if (val != null) {
//                                if (p != null)
//                                    p.val = val;
//                                else {
//                                    delta = 1;
//                                    t.putTreeVal(h, key, val);
//                                }
//                            }
//                            else if (p != null) {
//                                delta = -1;
//                                if (t.removeTreeNode(p))
//                                    setTabAt(tab, i, untreeify(t.first));
//                            }
//                        }
//                    }
//                }
//                if (binCount != 0) {
//                    if (binCount >= TREEIFY_THRESHOLD)
//                        treeifyBin(tab, i);
//                    break;
//                }
//            }
//        }
//        if (delta != 0)
//            addCount((long)delta, binCount);
//        return val;
//    }
//
//    // Hashtable legacy methods
//
//    /**
//     * Legacy method testing if some key maps into the specified value
//     * in this table.  This method is identical in functionality to
//     * {@link #containsValue(Object)}, and exists solely to ensure
//     * full compatibility with class {@link java.util.Hashtable},
//     * which supported this method prior to introduction of the
//     * Java Collections framework.
//     *
//     * @param  value a value to search for
//     * @return {@code true} if and only if some key maps to the
//     *         {@code value} argument in this table as
//     *         determined by the {@code equals} method;
//     *         {@code false} otherwise
//     * @throws NullPointerException if the specified value is null
//     */
//    public boolean contains(Object value) {
//        return containsValue(value);
//    }
//
//    /**
//     * Returns an enumeration of the keys in this table.
//     *
//     * @return an enumeration of the keys in this table
//     * @see #keySet()
//     */
//    public Enumeration<K> keys() {
//        Node<K,V>[] t;
//        int f = (t = table) == null ? 0 : t.length;
//        return new KeyIterator<K,V>(t, f, 0, f, this);
//    }
//
//    /**
//     * Returns an enumeration of the values in this table.
//     *
//     * @return an enumeration of the values in this table
//     * @see #values()
//     */
//    public Enumeration<V> elements() {
//        Node<K,V>[] t;
//        int f = (t = table) == null ? 0 : t.length;
//        return new ValueIterator<K,V>(t, f, 0, f, this);
//    }
//
//    // ConcurrentHashMap-only methods
//
//    /**
//     * Returns the number of mappings. This method should be used
//     * instead of {@link #size} because a ConcurrentHashMap may
//     * contain more mappings than can be represented as an int. The
//     * value returned is an estimate; the actual count may differ if
//     * there are concurrent insertions or removals.
//     *
//     * @return the number of mappings
//     * @since 1.8
//     */
//    public long mappingCount() {
//        long n = sumCount();
//        return (n < 0L) ? 0L : n; // ignore transient negative values
//    }
//
//    /**
//     * Creates a new {@link Set} backed by a ConcurrentHashMap
//     * from the given type to {@code Boolean.TRUE}.
//     *
//     * @param <K> the element type of the returned set
//     * @return the new set
//     * @since 1.8
//     */
//    public static <K> KeySetView<K,Boolean> newKeySet() {
//        return new KeySetView<K,Boolean>
//                (new ConcurrentHashMap18<K,Boolean>(), Boolean.TRUE);
//    }
//
//    /**
//     * Creates a new {@link Set} backed by a ConcurrentHashMap
//     * from the given type to {@code Boolean.TRUE}.
//     *
//     * @param initialCapacity The implementation performs internal
//     * sizing to accommodate this many elements.
//     * @param <K> the element type of the returned set
//     * @return the new set
//     * @throws IllegalArgumentException if the initial capacity of
//     * elements is negative
//     * @since 1.8
//     */
//    public static <K> KeySetView<K,Boolean> newKeySet(int initialCapacity) {
//        return new KeySetView<K,Boolean>
//                (new ConcurrentHashMap18<K,Boolean>(initialCapacity), Boolean.TRUE);
//    }
//
//    /**
//     * Returns a {@link Set} view of the keys in this map, using the
//     * given common mapped value for any additions (i.e., {@link
//     * Collection#add} and {@link Collection#addAll(Collection)}).
//     * This is of course only appropriate if it is acceptable to use
//     * the same value for all additions from this view.
//     *
//     * @param mappedValue the mapped value to use for any additions
//     * @return the set view
//     * @throws NullPointerException if the mappedValue is null
//     */
//    public KeySetView<K,V> keySet(V mappedValue) {
//        if (mappedValue == null)
//            throw new NullPointerException();
//        return new KeySetView<K,V>(this, mappedValue);
//    }
//
//    /* ---------------- Special Nodes -------------- */
//
//    /**
//     * A node inserted at head of bins during transfer operations.
//     */
//    static final class ForwardingNode<K,V> extends Node<K,V> {
//        final Node<K,V>[] nextTable;
//        ForwardingNode(Node<K,V>[] tab) {
//            super(MOVED, null, null, null);
//            this.nextTable = tab;
//        }
//
//        Node<K,V> find(int h, Object k) {
//            // loop to avoid arbitrarily deep recursion on forwarding nodes
//            outer: for (Node<K,V>[] tab = nextTable;;) {
//                Node<K,V> e; int n;
//                // 1. 判断新的数组是否是null，
//                // 2. 如果不为NULL给那就找到对应索引位上的头结点
//                // 3. 判断头节点是否为NULL
//                if (k == null || tab == null || (n = tab.length) == 0 ||
//                        (e = tabAt(tab, (n - 1) & h)) == null)
//                    return null;
//                // 自旋找节点
//                for (;;) {
//                    int eh; K ek;
//                    if ((eh = e.hash) == h &&
//                            ((ek = e.key) == k || (ek != null && k.equals(ek))))
//                        return e;
//                    if (eh < 0) {
//                        // 如果又变成了ForwardingNode标记节点，那说明有发生了扩容，需要跳出循环从新查找
//                        if (e instanceof ForwardingNode) {
//                            tab = ((ForwardingNode<K,V>)e).nextTable;
//                            continue outer;
//                        }
//                        else
//                            return e.find(h, k);
//                    }
//                    if ((e = e.next) == null)
//                        return null;
//                }
//            }
//        }
//    }
//
//    /**
//     * A place-holder node used in computeIfAbsent and compute
//     */
//    static final class ReservationNode<K,V> extends Node<K,V> {
//        ReservationNode() {
//            super(RESERVED, null, null, null);
//        }
//
//        Node<K,V> find(int h, Object k) {
//            return null;
//        }
//    }
//
//    /* ---------------- Table Initialization and Resizing -------------- */
//
//    /**
//     * Returns the stamp bits for resizing a table of size n.
//     * Must be negative when shifted left by RESIZE_STAMP_SHIFT.
//     */
//    static final int resizeStamp(int n) {
//        return Integer.numberOfLeadingZeros(n) | (1 << (RESIZE_STAMP_BITS - 1));
//    }
//
//    /**
//     * Initializes table, using the size recorded in sizeCtl.
//     */
//    private final Node<K,V>[] initTable() {
//        Node<K,V>[] tab; int sc;
//        while ((tab = table) == null || tab.length == 0) {
//            // 正在初始化
//            if ((sc = sizeCtl) < 0)
//                // 让出CPU执行权，然后自旋
//                Thread.yield(); // lost initialization race; just spin
//                // CAS替换标志位（相当于获取锁）
//            else if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
//                try {
//                    // 二次判断
//                    if ((tab = table) == null || tab.length == 0) {
//                        int n = (sc > 0) ? sc : DEFAULT_CAPACITY;
//                        @SuppressWarnings("unchecked")
//                        Node<K,V>[] nt = (Node<K,V>[])new Node<?,?>[n];
//                        table = tab = nt;
//                        // 相当于sc=n*3/4
//                        sc = n - (n >>> 2);
//                    }
//                } finally {
//                    // 扩容阈值
//                    sizeCtl = sc;
//                }
//                break;
//            }
//        }
//        return tab;
//    }
//
//    /**
//     * Adds to count, and if table is too small and not already
//     * resizing, initiates transfer. If already resizing, helps
//     * perform transfer if work is available.  Rechecks occupancy
//     * after a transfer to see if another resize is already needed
//     * because resizings are lagging additions.
//     *
//     * @param x the count to add
//     * @param check if <0, don't check resize, if <= 1 only check if uncontended
//     */
//    private final void addCount(long x, int check) {
//        // CounterCell[] as;使用计数器数组因该是为了提升并发量，减小冲突概率
//        CounterCell[] as; long b, s;
//        // 计数器数组不为NULL表示有多个线程在修改竞争修改baseCount值
//        if ((as = counterCells) != null ||
//                // 使用CAS更新baseCount的值（+1）如果失败说明存在竞争
//                !U.compareAndSwapLong(this, BASECOUNT, b = baseCount, s = b + x)) {
//            CounterCell a; long v; int m;
//            // 增量size（size++）是否存在竞争的标记位
//            boolean uncontended = true;
//            // CounterCell[] as为NULL表示增量size（size++）没有竞争
//            if (as == null || (m = as.length - 1) < 0 ||
//                    // 如果增量size（size++）存在竞争，我们会将size分层很多个桶（锁分离技术），然后随机取出一个桶来进行增量，主要目的是减小锁的竞争，提示并发量
//                    // 随机一个数组索引位（桶）来验证是否为NULL，如果a是null表示没有竞争
//                    (a = as[ThreadLocalRandom.getProbe() & m]) == null ||
//                    // CAS替换a的value，如果失败表示存在竞争
//                    !(uncontended =
//                            U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))) {
//                // 将size增量值存到as上
//                fullAddCount(x, uncontended);
//                return;
//            }
//            if (check <= 1)
//                return;
//            // 统计size
//            s = sumCount();
//        }
//        // 检查是否需要扩容
//        if (check >= 0) {
//            Node<K,V>[] tab, nt; int n, sc;
//            // size大于阈值sizeCtl，tab数组长度小于最大值1<<30
//            while (s >= (long)(sc = sizeCtl) && (tab = table) != null &&
//                    (n = tab.length) < MAXIMUM_CAPACITY) {
//                int rs = resizeStamp(n);
//                // 表示正在扩容
//                if (sc < 0) {
//                    if ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + 1 ||
//                            sc == rs + MAX_RESIZERS || (nt = nextTable) == null ||
//                            transferIndex <= 0)
//                        break;
//                    if (U.compareAndSwapInt(this, SIZECTL, sc, sc + 1))
//                        // 帮助扩容
//                        transfer(tab, nt);
//                }
//                // sc = (rs << RESIZE_STAMP_SHIFT) + 2，移位后是负数
//                else if (U.compareAndSwapInt(this, SIZECTL, sc,
//                        (rs << RESIZE_STAMP_SHIFT) + 2))
//                    // 发起扩容，此时nextTable=null
//                    transfer(tab, null);
//                s = sumCount();
//            }
//        }
//    }
//
//    /**
//     * Helps transfer if a resize is in progress.
//     */
//    final Node<K,V>[] helpTransfer(Node<K,V>[] tab, Node<K,V> f) {
//        Node<K,V>[] nextTab; int sc;
//        // ForwardingNode标记节点，表示正在扩容
//        if (tab != null && (f instanceof ForwardingNode) &&
//                (nextTab = ((ForwardingNode<K,V>)f).nextTable) != null) {
//            int rs = resizeStamp(tab.length);
//            while (nextTab == nextTable && table == tab &&
//                    (sc = sizeCtl) < 0) {
//                if ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + 1 ||
//                        sc == rs + MAX_RESIZERS || transferIndex <= 0)
//                    break;
//                if (U.compareAndSwapInt(this, SIZECTL, sc, sc + 1)) {
//                    transfer(tab, nextTab);
//                    break;
//                }
//            }
//            return nextTab;
//        }
//        return table;
//    }
//
//    /**
//     * Tries to presize table to accommodate the given number of elements.
//     *
//     * @param size number of elements (doesn't need to be perfectly accurate)
//     */
//    private final void tryPresize(int size) {
//        int c = (size >= (MAXIMUM_CAPACITY >>> 1)) ? MAXIMUM_CAPACITY :
//                tableSizeFor(size + (size >>> 1) + 1);
//        int sc;
//        while ((sc = sizeCtl) >= 0) {
//            Node<K,V>[] tab = table; int n;
//            if (tab == null || (n = tab.length) == 0) {
//                n = (sc > c) ? sc : c;
//                if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
//                    try {
//                        if (table == tab) {
//                            @SuppressWarnings("unchecked")
//                            Node<K,V>[] nt = (Node<K,V>[])new Node<?,?>[n];
//                            table = nt;
//                            sc = n - (n >>> 2);
//                        }
//                    } finally {
//                        sizeCtl = sc;
//                    }
//                }
//            }
//            else if (c <= sc || n >= MAXIMUM_CAPACITY)
//                break;
//            else if (tab == table) {
//                int rs = resizeStamp(n);
//                if (sc < 0) {
//                    Node<K,V>[] nt;
//                    if ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + 1 ||
//                            sc == rs + MAX_RESIZERS || (nt = nextTable) == null ||
//                            transferIndex <= 0)
//                        break;
//                    if (U.compareAndSwapInt(this, SIZECTL, sc, sc + 1))
//                        transfer(tab, nt);
//                }
//                else if (U.compareAndSwapInt(this, SIZECTL, sc,
//                        (rs << RESIZE_STAMP_SHIFT) + 2))
//                    transfer(tab, null);
//            }
//        }
//    }
//
//    /**
//     * Moves and/or copies the nodes in each bin to new table. See
//     * above for explanation.
//     */
//    private final void transfer(Node<K,V>[] tab, Node<K,V>[] nextTab) {
//        // n原来数组长度，stride步长
//        int n = tab.length, stride;
//        if ((stride = (NCPU > 1) ? (n >>> 3) / NCPU : n) < MIN_TRANSFER_STRIDE)
//            stride = MIN_TRANSFER_STRIDE; // subdivide range
//        // 第一个发起扩容的线程，需要初始化扩容后的数组
//        if (nextTab == null) {            // initiating
//            try {
//                @SuppressWarnings("unchecked")
//                Node<K,V>[] nt = (Node<K,V>[])new Node<?,?>[n << 1];
//                nextTab = nt;
//            } catch (Throwable ex) {      // try to cope with OOME
//                sizeCtl = Integer.MAX_VALUE;
//                return;
//            }
//            nextTable = nextTab;
//            transferIndex = n;
//        }
//        int nextn = nextTab.length;
//        // 扩容期间的数据节点（用于标志位，hash值是-1）
//        ForwardingNode<K,V> fwd = new ForwardingNode<K,V>(nextTab);
//        // 当advance == true时，表明该节点已经处理过了
//        boolean advance = true;
//        // 在扩容完成之前保证get不被影响
//        boolean finishing = false; // to ensure sweep before committing nextTab
//        //  在扩容前的数组上从右往左（从高索引位到低索引位）找到第一个有数据的索引位节点（有hash冲突的桶）,然后移动该索引位上所有节点数据
//        // 1. 如果找到的节点是NULL节点（没有hash冲突的节点），那么将该索引位的NULL替换成ForwardingNode标记节点，这个节点的hash是-1
//        // 2. 如果找到不为NULL的节点（有hash冲突的桶），则对这个节点进行加锁
//        // 3. 开始进进移动节点数据
//        for (int i = 0, bound = 0;;) {
//            //f:当前处理i位置的node（头结点或者根节点）;
//            Node<K,V> f; int fh;
//            // 通过while循环获取本次需要移动的节点索引i
//            while (advance) {
//                // nextIndex:下一个要处理的节点索引; nextBound:下一个需要处理的节点的索引边界
//                int nextIndex, nextBound;
//                // i是扩容前的数组索引位，通过--i来讲索引位往前一个索引位移动，直到0索引位
//                if (--i >= bound || finishing)
//                    advance = false;
//                    // 节点已全部转移
//                else if ((nextIndex = transferIndex) <= 0) {
//                    i = -1;
//                    advance = false;
//                }
//                // transferIndex（初值为最后一个节点的索引），表示从transferIndex开始后面所有的节点都已分配，
//                // 每次线程领取扩容任务后，需要更新transferIndex的值(transferIndex-stride)。
//                // CAS修改transferIndex，并更新索引边界
//                else if (U.compareAndSwapInt
//                        (this, TRANSFERINDEX, nextIndex,
//                                nextBound = (nextIndex > stride ?
//                                        nextIndex - stride : 0))) {
//                    bound = nextBound;
//                    // 扩容前数组最后一个索引位置
//                    i = nextIndex - 1;
//                    advance = false;
//                }
//            }
//            if (i < 0 || i >= n || i + n >= nextn) {
//                int sc;
//                // 已经完成所有节点复制了
//                if (finishing) {
//                    nextTable = null;
//                    table = nextTab;
//                    // sizeCtl阈值为原来的1.5倍
//                    sizeCtl = (n << 1) - (n >>> 1);
//                    // 结束自旋
//                    return;
//                }
//                // CAS 更新扩容阈值，在这里面sizectl值减一，说明新加入一个线程参与到扩容操作
//                if (U.compareAndSwapInt(this, SIZECTL, sc = sizeCtl, sc - 1)) {
//                    if ((sc - 2) != resizeStamp(n) << RESIZE_STAMP_SHIFT)
//                        return;
//                    finishing = advance = true;
//                    i = n; // recheck before commit
//                }
//            }
//            // 将以前扩容前的数组上为NULL的节点（还没有元素的桶或者说成没有hash冲突的数据节点），用ForwardingNode标记节点补齐
//            // 主要作用是：其他线程在put元素，发现找到的索引位是fwd节点则表示正在扩容，那么该线程会来帮助扩通，而不是在那里等待
//            else if ((f = tabAt(tab, i)) == null)
//                advance = casTabAt(tab, i, null, fwd);
//                // 表示处理过该节点了
//            else if ((fh = f.hash) == MOVED)
//                advance = true; // already processed
//            else {
//                // 对应索引位加锁
//                synchronized (f) {
//                    // 再次校验一下扩容前的数组对应索引位节点是否是我们找到的节点f
//                    if (tabAt(tab, i) == f) {
//                        // 低索引位头节点(i位)， 高位索引位头节点（i+tab.length）
//                        Node<K,V> ln, hn;
//                        // fh >=0 表示链表节点，TreeBin节点的hash值-2
//                        if (fh >= 0) {
//                            // fh & n算法可以算出新的节点该分配到那个索引位（runBit要么为0放低位ln，要么为n放高位hn），
//                            // runBit表示链表中最后一个元素的hash值&n的值
//                            int runBit = fh & n;
//                            // lastRun表示链表中最后一个元素
//                            Node<K,V> lastRun = f;
//                            // 找到链表中最后一个节点，并赋值给lastRun
//                            for (Node<K,V> p = f.next; p != null; p = p.next) {
//                                int b = p.hash & n;
//                                if (b != runBit) {
//                                    runBit = b;
//                                    lastRun = p;
//                                }
//                            }
//                            // 判断原来的最后一个节点应该添加到高位还是低位
//                            if (runBit == 0) {
//                                ln = lastRun;
//                                hn = null;
//                            }
//                            else {
//                                hn = lastRun;
//                                ln = null;
//                            }
//                            // f表示头结点，如果p不是尾节点，则转移节点
//                            // 如果以前节点顺序是 1 2 3 4 转移后就是 3 2 1 4
//                            for (Node<K,V> p = f; p != lastRun; p = p.next) {
//                                int ph = p.hash; K pk = p.key; V pv = p.val;
//                                if ((ph & n) == 0)
//                                    // 转移节点时都是新建节点,以免破坏原来数组结构影响get方法
//                                    ln = new Node<K,V>(ph, pk, pv, ln);
//                                else
//                                    hn = new Node<K,V>(ph, pk, pv, hn);
//                            }
//                            // 设置扩容后的数组低索引位头节点(i位)
//                            setTabAt(nextTab, i, ln);
//                            // 设置扩容后的数组高位索引位头节点（i+tab.length）
//                            setTabAt(nextTab, i + n, hn);
//                            // 设置扩容前的数组i位为标记节点，表示已经处理过了
//                            setTabAt(tab, i, fwd);
//                            advance = true;
//                        }
//                        else if (f instanceof TreeBin) {
//                            TreeBin<K,V> t = (TreeBin<K,V>)f;
//                            TreeNode<K,V> lo = null, loTail = null;
//                            TreeNode<K,V> hi = null, hiTail = null;
//                            int lc = 0, hc = 0;
//                            for (Node<K,V> e = t.first; e != null; e = e.next) {
//                                int h = e.hash;
//                                TreeNode<K,V> p = new TreeNode<K,V>
//                                        (h, e.key, e.val, null, null);
//                                if ((h & n) == 0) {
//                                    if ((p.prev = loTail) == null)
//                                        lo = p;
//                                    else
//                                        loTail.next = p;
//                                    loTail = p;
//                                    ++lc;
//                                }
//                                else {
//                                    if ((p.prev = hiTail) == null)
//                                        hi = p;
//                                    else
//                                        hiTail.next = p;
//                                    hiTail = p;
//                                    ++hc;
//                                }
//                            }
//                            ln = (lc <= UNTREEIFY_THRESHOLD) ? untreeify(lo) :
//                                    (hc != 0) ? new TreeBin<K,V>(lo) : t;
//                            hn = (hc <= UNTREEIFY_THRESHOLD) ? untreeify(hi) :
//                                    (lc != 0) ? new TreeBin<K,V>(hi) : t;
//                            // 设置扩容后的数组低索引位头节点(i位)
//                            setTabAt(nextTab, i, ln);
//                            // 设置扩容后的数组高位索引位头节点（i+tab.length）
//                            setTabAt(nextTab, i + n, hn);
//                            // 设置扩容前的数组i位为标记节点，表示已经处理过了
//                            setTabAt(tab, i, fwd);
//                            advance = true;
//                        }
//                    }
//                }
//            }
//        }
//    }
//
//    /* ---------------- Counter support -------------- */
//
//    /**
//     * A padded cell for distributing counts.  Adapted from LongAdder
//     * and Striped64.  See their internal docs for explanation.
//     */
//    @sun.misc.Contended static final class CounterCell {
//        volatile long value;
//        CounterCell(long x) { value = x; }
//    }
//
//    final long sumCount() {
//        CounterCell[] as = counterCells; CounterCell a;
//        long sum = baseCount;
//        if (as != null) {
//            for (int i = 0; i < as.length; ++i) {
//                if ((a = as[i]) != null)
//                    sum += a.value;
//            }
//        }
//        return sum;
//    }
//
//    // See LongAdder version for explanation
//    private final void fullAddCount(long x, boolean wasUncontended) {
//        int h;
//        if ((h = ThreadLocalRandom.getProbe()) == 0) {
//            ThreadLocalRandom.localInit();      // force initialization
//            h = ThreadLocalRandom.getProbe();
//            wasUncontended = true;
//        }
//        boolean collide = false;                // True if last slot nonempty
//        for (;;) {
//            CounterCell[] as; CounterCell a; int n; long v;
//            if ((as = counterCells) != null && (n = as.length) > 0) {
//                if ((a = as[(n - 1) & h]) == null) {
//                    if (cellsBusy == 0) {            // Try to attach new Cell
//                        CounterCell r = new CounterCell(x); // Optimistic create
//                        if (cellsBusy == 0 &&
//                                U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
//                            boolean created = false;
//                            try {               // Recheck under lock
//                                CounterCell[] rs; int m, j;
//                                if ((rs = counterCells) != null &&
//                                        (m = rs.length) > 0 &&
//                                        rs[j = (m - 1) & h] == null) {
//                                    rs[j] = r;
//                                    created = true;
//                                }
//                            } finally {
//                                cellsBusy = 0;
//                            }
//                            if (created)
//                                break;
//                            continue;           // Slot is now non-empty
//                        }
//                    }
//                    collide = false;
//                }
//                else if (!wasUncontended)       // CAS already known to fail
//                    wasUncontended = true;      // Continue after rehash
//                else if (U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))
//                    break;
//                else if (counterCells != as || n >= NCPU)
//                    collide = false;            // At max size or stale
//                else if (!collide)
//                    collide = true;
//                else if (cellsBusy == 0 &&
//                        U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
//                    try {
//                        if (counterCells == as) {// Expand table unless stale
//                            CounterCell[] rs = new CounterCell[n << 1];
//                            for (int i = 0; i < n; ++i)
//                                rs[i] = as[i];
//                            counterCells = rs;
//                        }
//                    } finally {
//                        cellsBusy = 0;
//                    }
//                    collide = false;
//                    continue;                   // Retry with expanded table
//                }
//                h = ThreadLocalRandom.advanceProbe(h);
//            }
//            else if (cellsBusy == 0 && counterCells == as &&
//                    U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
//                boolean init = false;
//                try {                           // Initialize table
//                    if (counterCells == as) {
//                        CounterCell[] rs = new CounterCell[2];
//                        rs[h & 1] = new CounterCell(x);
//                        counterCells = rs;
//                        init = true;
//                    }
//                } finally {
//                    cellsBusy = 0;
//                }
//                if (init)
//                    break;
//            }
//            else if (U.compareAndSwapLong(this, BASECOUNT, v = baseCount, v + x))
//                break;                          // Fall back on using base
//        }
//    }
//
//    /* ---------------- Conversion from/to TreeBins -------------- */
//
//    /**
//     * Replaces all linked nodes in bin at given index unless table is
//     * too small, in which case resizes instead.
//     */
//    private final void treeifyBin(Node<K,V>[] tab, int index) {
//        Node<K,V> b; int n, sc;
//        if (tab != null) {
//            if ((n = tab.length) < MIN_TREEIFY_CAPACITY)
//                tryPresize(n << 1);
//            else if ((b = tabAt(tab, index)) != null && b.hash >= 0) {
//                synchronized (b) {
//                    if (tabAt(tab, index) == b) {
//                        TreeNode<K,V> hd = null, tl = null;
//                        for (Node<K,V> e = b; e != null; e = e.next) {
//                            TreeNode<K,V> p =
//                                    new TreeNode<K,V>(e.hash, e.key, e.val,
//                                            null, null);
//                            if ((p.prev = tl) == null)
//                                hd = p;
//                            else
//                                tl.next = p;
//                            tl = p;
//                        }
//                        setTabAt(tab, index, new TreeBin<K,V>(hd));
//                    }
//                }
//            }
//        }
//    }
//
//    /**
//     * Returns a list on non-TreeNodes replacing those in given list.
//     */
//    static <K,V> Node<K,V> untreeify(Node<K,V> b) {
//        Node<K,V> hd = null, tl = null;
//        for (Node<K,V> q = b; q != null; q = q.next) {
//            Node<K,V> p = new Node<K,V>(q.hash, q.key, q.val, null);
//            if (tl == null)
//                hd = p;
//            else
//                tl.next = p;
//            tl = p;
//        }
//        return hd;
//    }
//
//    /* ---------------- TreeNodes -------------- */
//
//    /**
//     * Nodes for use in TreeBins
//     */
//    static final class TreeNode<K,V> extends Node<K,V> {
//        TreeNode<K,V> parent;  // red-black tree links
//        TreeNode<K,V> left;
//        TreeNode<K,V> right;
//        TreeNode<K,V> prev;    // needed to unlink next upon deletion
//        boolean red;
//
//        TreeNode(int hash, K key, V val, Node<K,V> next,
//                 TreeNode<K,V> parent) {
//            super(hash, key, val, next);
//            this.parent = parent;
//        }
//
//        Node<K,V> find(int h, Object k) {
//            return findTreeNode(h, k, null);
//        }
//
//        /**
//         * Returns the TreeNode (or null if not found) for the given key
//         * starting at given root.
//         */
//        final TreeNode<K,V> findTreeNode(int h, Object k, Class<?> kc) {
//            if (k != null) {
//                TreeNode<K,V> p = this;
//                do  {
//                    int ph, dir; K pk; TreeNode<K,V> q;
//                    TreeNode<K,V> pl = p.left, pr = p.right;
//                    if ((ph = p.hash) > h)
//                        p = pl;
//                    else if (ph < h)
//                        p = pr;
//                    else if ((pk = p.key) == k || (pk != null && k.equals(pk)))
//                        return p;
//                    else if (pl == null)
//                        p = pr;
//                    else if (pr == null)
//                        p = pl;
//                    else if ((kc != null ||
//                            (kc = comparableClassFor(k)) != null) &&
//                            (dir = compareComparables(kc, k, pk)) != 0)
//                        p = (dir < 0) ? pl : pr;
//                    else if ((q = pr.findTreeNode(h, k, kc)) != null)
//                        return q;
//                    else
//                        p = pl;
//                } while (p != null);
//            }
//            return null;
//        }
//    }
//
//    /* ---------------- TreeBins -------------- */
//
//    /**
//     * TreeNodes used at the heads of bins. TreeBins do not hold user
//     * keys or values, but instead point to list of TreeNodes and
//     * their root. They also maintain a parasitic read-write lock
//     * forcing writers (who hold bin lock) to wait for readers (who do
//     * not) to complete before tree restructuring operations.
//     */
//    static final class TreeBin<K,V> extends Node<K,V> {
//        TreeNode<K,V> root;
//        volatile TreeNode<K,V> first;
//        // 锁的持有者
//        volatile Thread waiter;
//        // 锁状态
//        volatile int lockState;
//        // values for lockState
//        // 表示持有写锁
//        static final int WRITER = 1; // set while holding write lock
//        // 表示等待
//        static final int WAITER = 2; // set when waiting for write lock
//        // 表示读锁的增量值
//        static final int READER = 4; // increment value for setting read lock
//
//        /**
//         * Tie-breaking utility for ordering insertions when equal
//         * hashCodes and non-comparable. We don't require a total
//         * order, just a consistent insertion rule to maintain
//         * equivalence across rebalancings. Tie-breaking further than
//         * necessary simplifies testing a bit.
//         */
//        static int tieBreakOrder(Object a, Object b) {
//            int d;
//            if (a == null || b == null ||
//                    (d = a.getClass().getName().
//                            compareTo(b.getClass().getName())) == 0)
//                d = (System.identityHashCode(a) <= System.identityHashCode(b) ?
//                        -1 : 1);
//            return d;
//        }
//
//        /**
//         * Creates bin with initial set of nodes headed by b.
//         */
//        TreeBin(TreeNode<K,V> b) {
//            super(TREEBIN, null, null, null);
//            this.first = b;
//            TreeNode<K,V> r = null;
//            for (TreeNode<K,V> x = b, next; x != null; x = next) {
//                next = (TreeNode<K,V>)x.next;
//                x.left = x.right = null;
//                if (r == null) {
//                    x.parent = null;
//                    x.red = false;
//                    r = x;
//                }
//                else {
//                    K k = x.key;
//                    int h = x.hash;
//                    Class<?> kc = null;
//                    for (TreeNode<K,V> p = r;;) {
//                        int dir, ph;
//                        K pk = p.key;
//                        if ((ph = p.hash) > h)
//                            dir = -1;
//                        else if (ph < h)
//                            dir = 1;
//                        else if ((kc == null &&
//                                (kc = comparableClassFor(k)) == null) ||
//                                (dir = compareComparables(kc, k, pk)) == 0)
//                            dir = tieBreakOrder(k, pk);
//                        TreeNode<K,V> xp = p;
//                        if ((p = (dir <= 0) ? p.left : p.right) == null) {
//                            x.parent = xp;
//                            if (dir <= 0)
//                                xp.left = x;
//                            else
//                                xp.right = x;
//                            r = balanceInsertion(r, x);
//                            break;
//                        }
//                    }
//                }
//            }
//            this.root = r;
//            assert checkInvariants(root);
//        }
//
//        /**
//         * Acquires write lock for tree restructuring.
//         */
//        private final void lockRoot() {
//            if (!U.compareAndSwapInt(this, LOCKSTATE, 0, WRITER))
//                contendedLock(); // offload to separate method
//        }
//
//        /**
//         * Releases write lock for tree restructuring.
//         */
//        private final void unlockRoot() {
//            lockState = 0;
//        }
//
//        /**
//         * Possibly blocks awaiting root lock.
//         */
//        private final void contendedLock() {
//            boolean waiting = false;
//            for (int s;;) {
//                if (((s = lockState) & ~WAITER) == 0) {
//                    if (U.compareAndSwapInt(this, LOCKSTATE, s, WRITER)) {
//                        if (waiting)
//                            waiter = null;
//                        return;
//                    }
//                }
//                else if ((s & WAITER) == 0) {
//                    if (U.compareAndSwapInt(this, LOCKSTATE, s, s | WAITER)) {
//                        waiting = true;
//                        waiter = Thread.currentThread();
//                    }
//                }
//                else if (waiting)
//                    LockSupport.park(this);
//            }
//        }
//
//        /**
//         * Returns matching node or null if none. Tries to search
//         * using tree comparisons from root, but continues linear
//         * search when lock not available.
//         */
//        final Node<K,V> find(int h, Object k) {
//            if (k != null) {
//                for (Node<K,V> e = first; e != null; ) {
//                    int s; K ek;
//                    if (((s = lockState) & (WAITER|WRITER)) != 0) {
//                        if (e.hash == h &&
//                                ((ek = e.key) == k || (ek != null && k.equals(ek))))
//                            return e;
//                        e = e.next;
//                    }
//                    else if (U.compareAndSwapInt(this, LOCKSTATE, s,
//                            s + READER)) {
//                        TreeNode<K,V> r, p;
//                        try {
//                            p = ((r = root) == null ? null :
//                                    r.findTreeNode(h, k, null));
//                        } finally {
//                            Thread w;
//                            if (U.getAndAddInt(this, LOCKSTATE, -READER) ==
//                                    (READER|WAITER) && (w = waiter) != null)
//                                LockSupport.unpark(w);
//                        }
//                        return p;
//                    }
//                }
//            }
//            return null;
//        }
//
//        /**
//         * Finds or adds a node.
//         * @return null if added
//         */
//        final TreeNode<K,V> putTreeVal(int h, K k, V v) {
//            Class<?> kc = null;
//            boolean searched = false;
//            for (TreeNode<K,V> p = root;;) {
//                int dir, ph; K pk;
//                if (p == null) {
//                    first = root = new TreeNode<K,V>(h, k, v, null, null);
//                    break;
//                }
//                else if ((ph = p.hash) > h)
//                    dir = -1;
//                else if (ph < h)
//                    dir = 1;
//                else if ((pk = p.key) == k || (pk != null && k.equals(pk)))
//                    return p;
//                else if ((kc == null &&
//                        (kc = comparableClassFor(k)) == null) ||
//                        (dir = compareComparables(kc, k, pk)) == 0) {
//                    if (!searched) {
//                        TreeNode<K,V> q, ch;
//                        searched = true;
//                        if (((ch = p.left) != null &&
//                                (q = ch.findTreeNode(h, k, kc)) != null) ||
//                                ((ch = p.right) != null &&
//                                        (q = ch.findTreeNode(h, k, kc)) != null))
//                            return q;
//                    }
//                    dir = tieBreakOrder(k, pk);
//                }
//
//                TreeNode<K,V> xp = p;
//                if ((p = (dir <= 0) ? p.left : p.right) == null) {
//                    TreeNode<K,V> x, f = first;
//                    first = x = new TreeNode<K,V>(h, k, v, f, xp);
//                    if (f != null)
//                        f.prev = x;
//                    if (dir <= 0)
//                        xp.left = x;
//                    else
//                        xp.right = x;
//                    if (!xp.red)
//                        x.red = true;
//                    else {
//                        lockRoot();
//                        try {
//                            root = balanceInsertion(root, x);
//                        } finally {
//                            unlockRoot();
//                        }
//                    }
//                    break;
//                }
//            }
//            assert checkInvariants(root);
//            return null;
//        }
//
//        /**
//         * Removes the given node, that must be present before this
//         * call.  This is messier than typical red-black deletion code
//         * because we cannot swap the contents of an interior node
//         * with a leaf successor that is pinned by "next" pointers
//         * that are accessible independently of lock. So instead we
//         * swap the tree linkages.
//         *
//         * @return true if now too small, so should be untreeified
//         */
//        final boolean removeTreeNode(TreeNode<K,V> p) {
//            TreeNode<K,V> next = (TreeNode<K,V>)p.next;
//            TreeNode<K,V> pred = p.prev;  // unlink traversal pointers
//            TreeNode<K,V> r, rl;
//            if (pred == null)
//                first = next;
//            else
//                pred.next = next;
//            if (next != null)
//                next.prev = pred;
//            if (first == null) {
//                root = null;
//                return true;
//            }
//            if ((r = root) == null || r.right == null || // too small
//                    (rl = r.left) == null || rl.left == null)
//                return true;
//            lockRoot();
//            try {
//                TreeNode<K,V> replacement;
//                TreeNode<K,V> pl = p.left;
//                TreeNode<K,V> pr = p.right;
//                if (pl != null && pr != null) {
//                    TreeNode<K,V> s = pr, sl;
//                    while ((sl = s.left) != null) // find successor
//                        s = sl;
//                    boolean c = s.red; s.red = p.red; p.red = c; // swap colors
//                    TreeNode<K,V> sr = s.right;
//                    TreeNode<K,V> pp = p.parent;
//                    if (s == pr) { // p was s's direct parent
//                        p.parent = s;
//                        s.right = p;
//                    }
//                    else {
//                        TreeNode<K,V> sp = s.parent;
//                        if ((p.parent = sp) != null) {
//                            if (s == sp.left)
//                                sp.left = p;
//                            else
//                                sp.right = p;
//                        }
//                        if ((s.right = pr) != null)
//                            pr.parent = s;
//                    }
//                    p.left = null;
//                    if ((p.right = sr) != null)
//                        sr.parent = p;
//                    if ((s.left = pl) != null)
//                        pl.parent = s;
//                    if ((s.parent = pp) == null)
//                        r = s;
//                    else if (p == pp.left)
//                        pp.left = s;
//                    else
//                        pp.right = s;
//                    if (sr != null)
//                        replacement = sr;
//                    else
//                        replacement = p;
//                }
//                else if (pl != null)
//                    replacement = pl;
//                else if (pr != null)
//                    replacement = pr;
//                else
//                    replacement = p;
//                if (replacement != p) {
//                    TreeNode<K,V> pp = replacement.parent = p.parent;
//                    if (pp == null)
//                        r = replacement;
//                    else if (p == pp.left)
//                        pp.left = replacement;
//                    else
//                        pp.right = replacement;
//                    p.left = p.right = p.parent = null;
//                }
//
//                root = (p.red) ? r : balanceDeletion(r, replacement);
//
//                if (p == replacement) {  // detach pointers
//                    TreeNode<K,V> pp;
//                    if ((pp = p.parent) != null) {
//                        if (p == pp.left)
//                            pp.left = null;
//                        else if (p == pp.right)
//                            pp.right = null;
//                        p.parent = null;
//                    }
//                }
//            } finally {
//                unlockRoot();
//            }
//            assert checkInvariants(root);
//            return false;
//        }
//
//        /* ------------------------------------------------------------ */
//        // Red-black tree methods, all adapted from CLR
//
//        static <K,V> TreeNode<K,V> rotateLeft(TreeNode<K,V> root,
//                                              TreeNode<K,V> p) {
//            TreeNode<K,V> r, pp, rl;
//            if (p != null && (r = p.right) != null) {
//                if ((rl = p.right = r.left) != null)
//                    rl.parent = p;
//                if ((pp = r.parent = p.parent) == null)
//                    (root = r).red = false;
//                else if (pp.left == p)
//                    pp.left = r;
//                else
//                    pp.right = r;
//                r.left = p;
//                p.parent = r;
//            }
//            return root;
//        }
//
//        static <K,V> TreeNode<K,V> rotateRight(TreeNode<K,V> root,
//                                               TreeNode<K,V> p) {
//            TreeNode<K,V> l, pp, lr;
//            if (p != null && (l = p.left) != null) {
//                if ((lr = p.left = l.right) != null)
//                    lr.parent = p;
//                if ((pp = l.parent = p.parent) == null)
//                    (root = l).red = false;
//                else if (pp.right == p)
//                    pp.right = l;
//                else
//                    pp.left = l;
//                l.right = p;
//                p.parent = l;
//            }
//            return root;
//        }
//
//        static <K,V> TreeNode<K,V> balanceInsertion(TreeNode<K,V> root,
//                                                    TreeNode<K,V> x) {
//            x.red = true;
//            for (TreeNode<K,V> xp, xpp, xppl, xppr;;) {
//                if ((xp = x.parent) == null) {
//                    x.red = false;
//                    return x;
//                }
//                else if (!xp.red || (xpp = xp.parent) == null)
//                    return root;
//                if (xp == (xppl = xpp.left)) {
//                    if ((xppr = xpp.right) != null && xppr.red) {
//                        xppr.red = false;
//                        xp.red = false;
//                        xpp.red = true;
//                        x = xpp;
//                    }
//                    else {
//                        if (x == xp.right) {
//                            root = rotateLeft(root, x = xp);
//                            xpp = (xp = x.parent) == null ? null : xp.parent;
//                        }
//                        if (xp != null) {
//                            xp.red = false;
//                            if (xpp != null) {
//                                xpp.red = true;
//                                root = rotateRight(root, xpp);
//                            }
//                        }
//                    }
//                }
//                else {
//                    if (xppl != null && xppl.red) {
//                        xppl.red = false;
//                        xp.red = false;
//                        xpp.red = true;
//                        x = xpp;
//                    }
//                    else {
//                        if (x == xp.left) {
//                            root = rotateRight(root, x = xp);
//                            xpp = (xp = x.parent) == null ? null : xp.parent;
//                        }
//                        if (xp != null) {
//                            xp.red = false;
//                            if (xpp != null) {
//                                xpp.red = true;
//                                root = rotateLeft(root, xpp);
//                            }
//                        }
//                    }
//                }
//            }
//        }
//
//        static <K,V> TreeNode<K,V> balanceDeletion(TreeNode<K,V> root,
//                                                   TreeNode<K,V> x) {
//            for (TreeNode<K,V> xp, xpl, xpr;;)  {
//                if (x == null || x == root)
//                    return root;
//                else if ((xp = x.parent) == null) {
//                    x.red = false;
//                    return x;
//                }
//                else if (x.red) {
//                    x.red = false;
//                    return root;
//                }
//                else if ((xpl = xp.left) == x) {
//                    if ((xpr = xp.right) != null && xpr.red) {
//                        xpr.red = false;
//                        xp.red = true;
//                        root = rotateLeft(root, xp);
//                        xpr = (xp = x.parent) == null ? null : xp.right;
//                    }
//                    if (xpr == null)
//                        x = xp;
//                    else {
//                        TreeNode<K,V> sl = xpr.left, sr = xpr.right;
//                        if ((sr == null || !sr.red) &&
//                                (sl == null || !sl.red)) {
//                            xpr.red = true;
//                            x = xp;
//                        }
//                        else {
//                            if (sr == null || !sr.red) {
//                                if (sl != null)
//                                    sl.red = false;
//                                xpr.red = true;
//                                root = rotateRight(root, xpr);
//                                xpr = (xp = x.parent) == null ?
//                                        null : xp.right;
//                            }
//                            if (xpr != null) {
//                                xpr.red = (xp == null) ? false : xp.red;
//                                if ((sr = xpr.right) != null)
//                                    sr.red = false;
//                            }
//                            if (xp != null) {
//                                xp.red = false;
//                                root = rotateLeft(root, xp);
//                            }
//                            x = root;
//                        }
//                    }
//                }
//                else { // symmetric
//                    if (xpl != null && xpl.red) {
//                        xpl.red = false;
//                        xp.red = true;
//                        root = rotateRight(root, xp);
//                        xpl = (xp = x.parent) == null ? null : xp.left;
//                    }
//                    if (xpl == null)
//                        x = xp;
//                    else {
//                        TreeNode<K,V> sl = xpl.left, sr = xpl.right;
//                        if ((sl == null || !sl.red) &&
//                                (sr == null || !sr.red)) {
//                            xpl.red = true;
//                            x = xp;
//                        }
//                        else {
//                            if (sl == null || !sl.red) {
//                                if (sr != null)
//                                    sr.red = false;
//                                xpl.red = true;
//                                root = rotateLeft(root, xpl);
//                                xpl = (xp = x.parent) == null ?
//                                        null : xp.left;
//                            }
//                            if (xpl != null) {
//                                xpl.red = (xp == null) ? false : xp.red;
//                                if ((sl = xpl.left) != null)
//                                    sl.red = false;
//                            }
//                            if (xp != null) {
//                                xp.red = false;
//                                root = rotateRight(root, xp);
//                            }
//                            x = root;
//                        }
//                    }
//                }
//            }
//        }
//
//        /**
//         * Recursive invariant check
//         */
//        static <K,V> boolean checkInvariants(TreeNode<K,V> t) {
//            TreeNode<K,V> tp = t.parent, tl = t.left, tr = t.right,
//                    tb = t.prev, tn = (TreeNode<K,V>)t.next;
//            if (tb != null && tb.next != t)
//                return false;
//            if (tn != null && tn.prev != t)
//                return false;
//            if (tp != null && t != tp.left && t != tp.right)
//                return false;
//            if (tl != null && (tl.parent != t || tl.hash > t.hash))
//                return false;
//            if (tr != null && (tr.parent != t || tr.hash < t.hash))
//                return false;
//            if (t.red && tl != null && tl.red && tr != null && tr.red)
//                return false;
//            if (tl != null && !checkInvariants(tl))
//                return false;
//            if (tr != null && !checkInvariants(tr))
//                return false;
//            return true;
//        }
//
//        private static final sun.misc.Unsafe U;
//        private static final long LOCKSTATE;
//        static {
//            try {
//                U = sun.misc.Unsafe.getUnsafe();
//                Class<?> k = TreeBin.class;
//                LOCKSTATE = U.objectFieldOffset
//                        (k.getDeclaredField("lockState"));
//            } catch (Exception e) {
//                throw new Error(e);
//            }
//        }
//    }
//
//    /* ----------------Table Traversal -------------- */
//
//    /**
//     * Records the table, its length, and current traversal index for a
//     * traverser that must process a region of a forwarded table before
//     * proceeding with current table.
//     */
//    static final class TableStack<K,V> {
//        int length;
//        int index;
//        Node<K,V>[] tab;
//        TableStack<K,V> next;
//    }
//
//    /**
//     * Encapsulates traversal for methods such as containsValue; also
//     * serves as a base class for other iterators and spliterators.
//     *
//     * Method advance visits once each still-valid node that was
//     * reachable upon iterator construction. It might miss some that
//     * were added to a bin after the bin was visited, which is OK wrt
//     * consistency guarantees. Maintaining this property in the face
//     * of possible ongoing resizes requires a fair amount of
//     * bookkeeping state that is difficult to optimize away amidst
//     * volatile accesses.  Even so, traversal maintains reasonable
//     * throughput.
//     *
//     * Normally, iteration proceeds bin-by-bin traversing lists.
//     * However, if the table has been resized, then all future steps
//     * must traverse both the bin at the current index as well as at
//     * (index + baseSize); and so on for further resizings. To
//     * paranoically cope with potential sharing by users of iterators
//     * across threads, iteration terminates if a bounds checks fails
//     * for a table read.
//     */
//    static class Traverser<K,V> {
//        Node<K,V>[] tab;        // current table; updated if resized
//        Node<K,V> next;         // the next entry to use
//        TableStack<K,V> stack, spare; // to save/restore on ForwardingNodes
//        int index;              // index of bin to use next
//        int baseIndex;          // current index of initial table
//        int baseLimit;          // index bound for initial table
//        final int baseSize;     // initial table size
//
//        Traverser(Node<K,V>[] tab, int size, int index, int limit) {
//            this.tab = tab;
//            this.baseSize = size;
//            this.baseIndex = this.index = index;
//            this.baseLimit = limit;
//            this.next = null;
//        }
//
//        /**
//         * Advances if possible, returning next valid node, or null if none.
//         */
//        final Node<K,V> advance() {
//            Node<K,V> e;
//            if ((e = next) != null)
//                e = e.next;
//            for (;;) {
//                Node<K,V>[] t; int i, n;  // must use locals in checks
//                if (e != null)
//                    return next = e;
//                if (baseIndex >= baseLimit || (t = tab) == null ||
//                        (n = t.length) <= (i = index) || i < 0)
//                    return next = null;
//                if ((e = tabAt(t, i)) != null && e.hash < 0) {
//                    if (e instanceof ForwardingNode) {
//                        tab = ((ForwardingNode<K,V>)e).nextTable;
//                        e = null;
//                        pushState(t, i, n);
//                        continue;
//                    }
//                    else if (e instanceof TreeBin)
//                        e = ((TreeBin<K,V>)e).first;
//                    else
//                        e = null;
//                }
//                if (stack != null)
//                    recoverState(n);
//                else if ((index = i + baseSize) >= n)
//                    index = ++baseIndex; // visit upper slots if present
//            }
//        }
//
//        /**
//         * Saves traversal state upon encountering a forwarding node.
//         */
//        private void pushState(Node<K,V>[] t, int i, int n) {
//            TableStack<K,V> s = spare;  // reuse if possible
//            if (s != null)
//                spare = s.next;
//            else
//                s = new TableStack<K,V>();
//            s.tab = t;
//            s.length = n;
//            s.index = i;
//            s.next = stack;
//            stack = s;
//        }
//
//        /**
//         * Possibly pops traversal state.
//         *
//         * @param n length of current table
//         */
//        private void recoverState(int n) {
//            TableStack<K,V> s; int len;
//            while ((s = stack) != null && (index += (len = s.length)) >= n) {
//                n = len;
//                index = s.index;
//                tab = s.tab;
//                s.tab = null;
//                TableStack<K,V> next = s.next;
//                s.next = spare; // save for reuse
//                stack = next;
//                spare = s;
//            }
//            if (s == null && (index += baseSize) >= n)
//                index = ++baseIndex;
//        }
//    }
//
//    /**
//     * Base of key, value, and entry Iterators. Adds fields to
//     * Traverser to support iterator.remove.
//     */
//    static class BaseIterator<K,V> extends Traverser<K,V> {
//        final ConcurrentHashMap18<K,V> map;
//        Node<K,V> lastReturned;
//        BaseIterator(Node<K,V>[] tab, int size, int index, int limit,
//                     ConcurrentHashMap18<K,V> map) {
//            super(tab, size, index, limit);
//            this.map = map;
//            advance();
//        }
//
//        public final boolean hasNext() { return next != null; }
//        public final boolean hasMoreElements() { return next != null; }
//
//        public final void remove() {
//            Node<K,V> p;
//            if ((p = lastReturned) == null)
//                throw new IllegalStateException();
//            lastReturned = null;
//            map.replaceNode(p.key, null, null);
//        }
//    }
//
//    static final class KeyIterator<K,V> extends BaseIterator<K,V>
//            implements Iterator<K>, Enumeration<K> {
//        KeyIterator(Node<K,V>[] tab, int index, int size, int limit,
//                    ConcurrentHashMap18<K,V> map) {
//            super(tab, index, size, limit, map);
//        }
//
//        public final K next() {
//            Node<K,V> p;
//            if ((p = next) == null)
//                throw new NoSuchElementException();
//            K k = p.key;
//            lastReturned = p;
//            advance();
//            return k;
//        }
//
//        public final K nextElement() { return next(); }
//    }
//
//    static final class ValueIterator<K,V> extends BaseIterator<K,V>
//            implements Iterator<V>, Enumeration<V> {
//        ValueIterator(Node<K,V>[] tab, int index, int size, int limit,
//                      ConcurrentHashMap18<K,V> map) {
//            super(tab, index, size, limit, map);
//        }
//
//        public final V next() {
//            Node<K,V> p;
//            if ((p = next) == null)
//                throw new NoSuchElementException();
//            V v = p.val;
//            lastReturned = p;
//            advance();
//            return v;
//        }
//
//        public final V nextElement() { return next(); }
//    }
//
//    static final class EntryIterator<K,V> extends BaseIterator<K,V>
//            implements Iterator<Map.Entry<K,V>> {
//        EntryIterator(Node<K,V>[] tab, int index, int size, int limit,
//                      ConcurrentHashMap18<K,V> map) {
//            super(tab, index, size, limit, map);
//        }
//
//        public final Map.Entry<K,V> next() {
//            Node<K,V> p;
//            if ((p = next) == null)
//                throw new NoSuchElementException();
//            K k = p.key;
//            V v = p.val;
//            lastReturned = p;
//            advance();
//            return new MapEntry<K,V>(k, v, map);
//        }
//    }
//
//    /**
//     * Exported Entry for EntryIterator
//     */
//    static final class MapEntry<K,V> implements Map.Entry<K,V> {
//        final K key; // non-null
//        V val;       // non-null
//        final ConcurrentHashMap18<K,V> map;
//        MapEntry(K key, V val, ConcurrentHashMap18<K,V> map) {
//            this.key = key;
//            this.val = val;
//            this.map = map;
//        }
//        public K getKey()        { return key; }
//        public V getValue()      { return val; }
//        public int hashCode()    { return key.hashCode() ^ val.hashCode(); }
//        public String toString() { return key + "=" + val; }
//
//        public boolean equals(Object o) {
//            Object k, v; Map.Entry<?,?> e;
//            return ((o instanceof Map.Entry) &&
//                    (k = (e = (Map.Entry<?,?>)o).getKey()) != null &&
//                    (v = e.getValue()) != null &&
//                    (k == key || k.equals(key)) &&
//                    (v == val || v.equals(val)));
//        }
//
//        /**
//         * Sets our entry's value and writes through to the map. The
//         * value to return is somewhat arbitrary here. Since we do not
//         * necessarily track asynchronous changes, the most recent
//         * "previous" value could be different from what we return (or
//         * could even have been removed, in which case the put will
//         * re-establish). We do not and cannot guarantee more.
//         */
//        public V setValue(V value) {
//            if (value == null) throw new NullPointerException();
//            V v = val;
//            val = value;
//            map.put(key, value);
//            return v;
//        }
//    }
//
//    static final class KeySpliterator<K,V> extends Traverser<K,V>
//            implements Spliterator<K> {
//        long est;               // size estimate
//        KeySpliterator(Node<K,V>[] tab, int size, int index, int limit,
//                       long est) {
//            super(tab, size, index, limit);
//            this.est = est;
//        }
//
//        public Spliterator<K> trySplit() {
//            int i, f, h;
//            return (h = ((i = baseIndex) + (f = baseLimit)) >>> 1) <= i ? null :
//                    new KeySpliterator<K,V>(tab, baseSize, baseLimit = h,
//                            f, est >>>= 1);
//        }
//
//        public void forEachRemaining(Consumer<? super K> action) {
//            if (action == null) throw new NullPointerException();
//            for (Node<K,V> p; (p = advance()) != null;)
//                action.accept(p.key);
//        }
//
//        public boolean tryAdvance(Consumer<? super K> action) {
//            if (action == null) throw new NullPointerException();
//            Node<K,V> p;
//            if ((p = advance()) == null)
//                return false;
//            action.accept(p.key);
//            return true;
//        }
//
//        public long estimateSize() { return est; }
//
//        public int characteristics() {
//            return Spliterator.DISTINCT | Spliterator.CONCURRENT |
//                    Spliterator.NONNULL;
//        }
//    }
//
//    static final class ValueSpliterator<K,V> extends Traverser<K,V>
//            implements Spliterator<V> {
//        long est;               // size estimate
//        ValueSpliterator(Node<K,V>[] tab, int size, int index, int limit,
//                         long est) {
//            super(tab, size, index, limit);
//            this.est = est;
//        }
//
//        public Spliterator<V> trySplit() {
//            int i, f, h;
//            return (h = ((i = baseIndex) + (f = baseLimit)) >>> 1) <= i ? null :
//                    new ValueSpliterator<K,V>(tab, baseSize, baseLimit = h,
//                            f, est >>>= 1);
//        }
//
//        public void forEachRemaining(Consumer<? super V> action) {
//            if (action == null) throw new NullPointerException();
//            for (Node<K,V> p; (p = advance()) != null;)
//                action.accept(p.val);
//        }
//
//        public boolean tryAdvance(Consumer<? super V> action) {
//            if (action == null) throw new NullPointerException();
//            Node<K,V> p;
//            if ((p = advance()) == null)
//                return false;
//            action.accept(p.val);
//            return true;
//        }
//
//        public long estimateSize() { return est; }
//
//        public int characteristics() {
//            return Spliterator.CONCURRENT | Spliterator.NONNULL;
//        }
//    }
//
//    static final class EntrySpliterator<K,V> extends Traverser<K,V>
//            implements Spliterator<Map.Entry<K,V>> {
//        final ConcurrentHashMap18<K,V> map; // To export MapEntry
//        long est;               // size estimate
//        EntrySpliterator(Node<K,V>[] tab, int size, int index, int limit,
//                         long est, ConcurrentHashMap18<K,V> map) {
//            super(tab, size, index, limit);
//            this.map = map;
//            this.est = est;
//        }
//
//        public Spliterator<Map.Entry<K,V>> trySplit() {
//            int i, f, h;
//            return (h = ((i = baseIndex) + (f = baseLimit)) >>> 1) <= i ? null :
//                    new EntrySpliterator<K,V>(tab, baseSize, baseLimit = h,
//                            f, est >>>= 1, map);
//        }
//
//        public void forEachRemaining(Consumer<? super Map.Entry<K,V>> action) {
//            if (action == null) throw new NullPointerException();
//            for (Node<K,V> p; (p = advance()) != null; )
//                action.accept(new MapEntry<K,V>(p.key, p.val, map));
//        }
//
//        public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) {
//            if (action == null) throw new NullPointerException();
//            Node<K,V> p;
//            if ((p = advance()) == null)
//                return false;
//            action.accept(new MapEntry<K,V>(p.key, p.val, map));
//            return true;
//        }
//
//        public long estimateSize() { return est; }
//
//        public int characteristics() {
//            return Spliterator.DISTINCT | Spliterator.CONCURRENT |
//                    Spliterator.NONNULL;
//        }
//    }
//
//    // Parallel bulk operations
//
//    /**
//     * Computes initial batch value for bulk tasks. The returned value
//     * is approximately exp2 of the number of times (minus one) to
//     * split task by two before executing leaf action. This value is
//     * faster to compute and more convenient to use as a guide to
//     * splitting than is the depth, since it is used while dividing by
//     * two anyway.
//     */
//    final int batchFor(long b) {
//        long n;
//        if (b == Long.MAX_VALUE || (n = sumCount()) <= 1L || n < b)
//            return 0;
//        int sp = ForkJoinPool.getCommonPoolParallelism() << 2; // slack of 4
//        return (b <= 0L || (n /= b) >= sp) ? sp : (int)n;
//    }
//
//    /**
//     * Performs the given action for each (key, value).
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param action the action
//     * @since 1.8
//     */
//    public void forEach(long parallelismThreshold,
//                        BiConsumer<? super K,? super V> action) {
//        if (action == null) throw new NullPointerException();
//        new ForEachMappingTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        action).invoke();
//    }
//
//    /**
//     * Performs the given action for each non-null transformation
//     * of each (key, value).
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element, or null if there is no transformation (in
//     * which case the action is not applied)
//     * @param action the action
//     * @param <U> the return type of the transformer
//     * @since 1.8
//     */
//    public <U> void forEach(long parallelismThreshold,
//                            BiFunction<? super K, ? super V, ? extends U> transformer,
//                            Consumer<? super U> action) {
//        if (transformer == null || action == null)
//            throw new NullPointerException();
//        new ForEachTransformedMappingTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        transformer, action).invoke();
//    }
//
//    /**
//     * Returns a non-null result from applying the given search
//     * function on each (key, value), or null if none.  Upon
//     * success, further element processing is suppressed and the
//     * results of any other parallel invocations of the search
//     * function are ignored.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param searchFunction a function returning a non-null
//     * result on success, else null
//     * @param <U> the return type of the search function
//     * @return a non-null result from applying the given search
//     * function on each (key, value), or null if none
//     * @since 1.8
//     */
//    public <U> U search(long parallelismThreshold,
//                        BiFunction<? super K, ? super V, ? extends U> searchFunction) {
//        if (searchFunction == null) throw new NullPointerException();
//        return new SearchMappingsTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        searchFunction, new AtomicReference<U>()).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all (key, value) pairs using the given reducer to
//     * combine values, or null if none.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element, or null if there is no transformation (in
//     * which case it is not combined)
//     * @param reducer a commutative associative combining function
//     * @param <U> the return type of the transformer
//     * @return the result of accumulating the given transformation
//     * of all (key, value) pairs
//     * @since 1.8
//     */
//    public <U> U reduce(long parallelismThreshold,
//                        BiFunction<? super K, ? super V, ? extends U> transformer,
//                        BiFunction<? super U, ? super U, ? extends U> reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceMappingsTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all (key, value) pairs using the given reducer to
//     * combine values, and the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all (key, value) pairs
//     * @since 1.8
//     */
//    public double reduceToDouble(long parallelismThreshold,
//                                 ToDoubleBiFunction<? super K, ? super V> transformer,
//                                 double basis,
//                                 DoubleBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceMappingsToDoubleTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all (key, value) pairs using the given reducer to
//     * combine values, and the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all (key, value) pairs
//     * @since 1.8
//     */
//    public long reduceToLong(long parallelismThreshold,
//                             ToLongBiFunction<? super K, ? super V> transformer,
//                             long basis,
//                             LongBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceMappingsToLongTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all (key, value) pairs using the given reducer to
//     * combine values, and the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all (key, value) pairs
//     * @since 1.8
//     */
//    public int reduceToInt(long parallelismThreshold,
//                           ToIntBiFunction<? super K, ? super V> transformer,
//                           int basis,
//                           IntBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceMappingsToIntTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//    /**
//     * Performs the given action for each key.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param action the action
//     * @since 1.8
//     */
//    public void forEachKey(long parallelismThreshold,
//                           Consumer<? super K> action) {
//        if (action == null) throw new NullPointerException();
//        new ForEachKeyTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        action).invoke();
//    }
//
//    /**
//     * Performs the given action for each non-null transformation
//     * of each key.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element, or null if there is no transformation (in
//     * which case the action is not applied)
//     * @param action the action
//     * @param <U> the return type of the transformer
//     * @since 1.8
//     */
//    public <U> void forEachKey(long parallelismThreshold,
//                               Function<? super K, ? extends U> transformer,
//                               Consumer<? super U> action) {
//        if (transformer == null || action == null)
//            throw new NullPointerException();
//        new ForEachTransformedKeyTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        transformer, action).invoke();
//    }
//
//    /**
//     * Returns a non-null result from applying the given search
//     * function on each key, or null if none. Upon success,
//     * further element processing is suppressed and the results of
//     * any other parallel invocations of the search function are
//     * ignored.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param searchFunction a function returning a non-null
//     * result on success, else null
//     * @param <U> the return type of the search function
//     * @return a non-null result from applying the given search
//     * function on each key, or null if none
//     * @since 1.8
//     */
//    public <U> U searchKeys(long parallelismThreshold,
//                            Function<? super K, ? extends U> searchFunction) {
//        if (searchFunction == null) throw new NullPointerException();
//        return new SearchKeysTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        searchFunction, new AtomicReference<U>()).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating all keys using the given
//     * reducer to combine values, or null if none.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating all keys using the given
//     * reducer to combine values, or null if none
//     * @since 1.8
//     */
//    public K reduceKeys(long parallelismThreshold,
//                        BiFunction<? super K, ? super K, ? extends K> reducer) {
//        if (reducer == null) throw new NullPointerException();
//        return new ReduceKeysTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all keys using the given reducer to combine values, or
//     * null if none.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element, or null if there is no transformation (in
//     * which case it is not combined)
//     * @param reducer a commutative associative combining function
//     * @param <U> the return type of the transformer
//     * @return the result of accumulating the given transformation
//     * of all keys
//     * @since 1.8
//     */
//    public <U> U reduceKeys(long parallelismThreshold,
//                            Function<? super K, ? extends U> transformer,
//                            BiFunction<? super U, ? super U, ? extends U> reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceKeysTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all keys using the given reducer to combine values, and
//     * the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all keys
//     * @since 1.8
//     */
//    public double reduceKeysToDouble(long parallelismThreshold,
//                                     ToDoubleFunction<? super K> transformer,
//                                     double basis,
//                                     DoubleBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceKeysToDoubleTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all keys using the given reducer to combine values, and
//     * the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all keys
//     * @since 1.8
//     */
//    public long reduceKeysToLong(long parallelismThreshold,
//                                 ToLongFunction<? super K> transformer,
//                                 long basis,
//                                 LongBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceKeysToLongTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all keys using the given reducer to combine values, and
//     * the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all keys
//     * @since 1.8
//     */
//    public int reduceKeysToInt(long parallelismThreshold,
//                               ToIntFunction<? super K> transformer,
//                               int basis,
//                               IntBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceKeysToIntTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//    /**
//     * Performs the given action for each value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param action the action
//     * @since 1.8
//     */
//    public void forEachValue(long parallelismThreshold,
//                             Consumer<? super V> action) {
//        if (action == null)
//            throw new NullPointerException();
//        new ForEachValueTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        action).invoke();
//    }
//
//    /**
//     * Performs the given action for each non-null transformation
//     * of each value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element, or null if there is no transformation (in
//     * which case the action is not applied)
//     * @param action the action
//     * @param <U> the return type of the transformer
//     * @since 1.8
//     */
//    public <U> void forEachValue(long parallelismThreshold,
//                                 Function<? super V, ? extends U> transformer,
//                                 Consumer<? super U> action) {
//        if (transformer == null || action == null)
//            throw new NullPointerException();
//        new ForEachTransformedValueTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        transformer, action).invoke();
//    }
//
//    /**
//     * Returns a non-null result from applying the given search
//     * function on each value, or null if none.  Upon success,
//     * further element processing is suppressed and the results of
//     * any other parallel invocations of the search function are
//     * ignored.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param searchFunction a function returning a non-null
//     * result on success, else null
//     * @param <U> the return type of the search function
//     * @return a non-null result from applying the given search
//     * function on each value, or null if none
//     * @since 1.8
//     */
//    public <U> U searchValues(long parallelismThreshold,
//                              Function<? super V, ? extends U> searchFunction) {
//        if (searchFunction == null) throw new NullPointerException();
//        return new SearchValuesTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        searchFunction, new AtomicReference<U>()).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating all values using the
//     * given reducer to combine values, or null if none.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating all values
//     * @since 1.8
//     */
//    public V reduceValues(long parallelismThreshold,
//                          BiFunction<? super V, ? super V, ? extends V> reducer) {
//        if (reducer == null) throw new NullPointerException();
//        return new ReduceValuesTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all values using the given reducer to combine values, or
//     * null if none.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element, or null if there is no transformation (in
//     * which case it is not combined)
//     * @param reducer a commutative associative combining function
//     * @param <U> the return type of the transformer
//     * @return the result of accumulating the given transformation
//     * of all values
//     * @since 1.8
//     */
//    public <U> U reduceValues(long parallelismThreshold,
//                              Function<? super V, ? extends U> transformer,
//                              BiFunction<? super U, ? super U, ? extends U> reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceValuesTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all values using the given reducer to combine values,
//     * and the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all values
//     * @since 1.8
//     */
//    public double reduceValuesToDouble(long parallelismThreshold,
//                                       ToDoubleFunction<? super V> transformer,
//                                       double basis,
//                                       DoubleBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceValuesToDoubleTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all values using the given reducer to combine values,
//     * and the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all values
//     * @since 1.8
//     */
//    public long reduceValuesToLong(long parallelismThreshold,
//                                   ToLongFunction<? super V> transformer,
//                                   long basis,
//                                   LongBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceValuesToLongTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all values using the given reducer to combine values,
//     * and the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all values
//     * @since 1.8
//     */
//    public int reduceValuesToInt(long parallelismThreshold,
//                                 ToIntFunction<? super V> transformer,
//                                 int basis,
//                                 IntBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceValuesToIntTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//    /**
//     * Performs the given action for each entry.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param action the action
//     * @since 1.8
//     */
//    public void forEachEntry(long parallelismThreshold,
//                             Consumer<? super Map.Entry<K,V>> action) {
//        if (action == null) throw new NullPointerException();
//        new ForEachEntryTask<K,V>(null, batchFor(parallelismThreshold), 0, 0, table,
//                action).invoke();
//    }
//
//    /**
//     * Performs the given action for each non-null transformation
//     * of each entry.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element, or null if there is no transformation (in
//     * which case the action is not applied)
//     * @param action the action
//     * @param <U> the return type of the transformer
//     * @since 1.8
//     */
//    public <U> void forEachEntry(long parallelismThreshold,
//                                 Function<Map.Entry<K,V>, ? extends U> transformer,
//                                 Consumer<? super U> action) {
//        if (transformer == null || action == null)
//            throw new NullPointerException();
//        new ForEachTransformedEntryTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        transformer, action).invoke();
//    }
//
//    /**
//     * Returns a non-null result from applying the given search
//     * function on each entry, or null if none.  Upon success,
//     * further element processing is suppressed and the results of
//     * any other parallel invocations of the search function are
//     * ignored.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param searchFunction a function returning a non-null
//     * result on success, else null
//     * @param <U> the return type of the search function
//     * @return a non-null result from applying the given search
//     * function on each entry, or null if none
//     * @since 1.8
//     */
//    public <U> U searchEntries(long parallelismThreshold,
//                               Function<Map.Entry<K,V>, ? extends U> searchFunction) {
//        if (searchFunction == null) throw new NullPointerException();
//        return new SearchEntriesTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        searchFunction, new AtomicReference<U>()).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating all entries using the
//     * given reducer to combine values, or null if none.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating all entries
//     * @since 1.8
//     */
//    public Map.Entry<K,V> reduceEntries(long parallelismThreshold,
//                                        BiFunction<Map.Entry<K,V>, Map.Entry<K,V>, ? extends Map.Entry<K,V>> reducer) {
//        if (reducer == null) throw new NullPointerException();
//        return new ReduceEntriesTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all entries using the given reducer to combine values,
//     * or null if none.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element, or null if there is no transformation (in
//     * which case it is not combined)
//     * @param reducer a commutative associative combining function
//     * @param <U> the return type of the transformer
//     * @return the result of accumulating the given transformation
//     * of all entries
//     * @since 1.8
//     */
//    public <U> U reduceEntries(long parallelismThreshold,
//                               Function<Map.Entry<K,V>, ? extends U> transformer,
//                               BiFunction<? super U, ? super U, ? extends U> reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceEntriesTask<K,V,U>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all entries using the given reducer to combine values,
//     * and the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all entries
//     * @since 1.8
//     */
//    public double reduceEntriesToDouble(long parallelismThreshold,
//                                        ToDoubleFunction<Map.Entry<K,V>> transformer,
//                                        double basis,
//                                        DoubleBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceEntriesToDoubleTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all entries using the given reducer to combine values,
//     * and the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all entries
//     * @since 1.8
//     */
//    public long reduceEntriesToLong(long parallelismThreshold,
//                                    ToLongFunction<Map.Entry<K,V>> transformer,
//                                    long basis,
//                                    LongBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceEntriesToLongTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//    /**
//     * Returns the result of accumulating the given transformation
//     * of all entries using the given reducer to combine values,
//     * and the given basis as an identity value.
//     *
//     * @param parallelismThreshold the (estimated) number of elements
//     * needed for this operation to be executed in parallel
//     * @param transformer a function returning the transformation
//     * for an element
//     * @param basis the identity (initial default value) for the reduction
//     * @param reducer a commutative associative combining function
//     * @return the result of accumulating the given transformation
//     * of all entries
//     * @since 1.8
//     */
//    public int reduceEntriesToInt(long parallelismThreshold,
//                                  ToIntFunction<Map.Entry<K,V>> transformer,
//                                  int basis,
//                                  IntBinaryOperator reducer) {
//        if (transformer == null || reducer == null)
//            throw new NullPointerException();
//        return new MapReduceEntriesToIntTask<K,V>
//                (null, batchFor(parallelismThreshold), 0, 0, table,
//                        null, transformer, basis, reducer).invoke();
//    }
//
//
//    /* ----------------Views -------------- */
//
//    /**
//     * Base class for views.
//     */
//    abstract static class CollectionView<K,V,E>
//            implements Collection<E>, java.io.Serializable {
//        private static final long serialVersionUID = 7249069246763182397L;
//        final ConcurrentHashMap18<K,V> map;
//        CollectionView(ConcurrentHashMap18<K,V> map)  { this.map = map; }
//
//        /**
//         * Returns the map backing this view.
//         *
//         * @return the map backing this view
//         */
//        public ConcurrentHashMap18<K,V> getMap() { return map; }
//
//        /**
//         * Removes all of the elements from this view, by removing all
//         * the mappings from the map backing this view.
//         */
//        public final void clear()      { map.clear(); }
//        public final int size()        { return map.size(); }
//        public final boolean isEmpty() { return map.isEmpty(); }
//
//        // implementations below rely on concrete classes supplying these
//        // abstract methods
//        /**
//         * Returns an iterator over the elements in this collection.
//         *
//         * <p>The returned iterator is
//         * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
//         *
//         * @return an iterator over the elements in this collection
//         */
//        public abstract Iterator<E> iterator();
//        public abstract boolean contains(Object o);
//        public abstract boolean remove(Object o);
//
//        private static final String oomeMsg = "Required array size too large";
//
//        public final Object[] toArray() {
//            long sz = map.mappingCount();
//            if (sz > MAX_ARRAY_SIZE)
//                throw new OutOfMemoryError(oomeMsg);
//            int n = (int)sz;
//            Object[] r = new Object[n];
//            int i = 0;
//            for (E e : this) {
//                if (i == n) {
//                    if (n >= MAX_ARRAY_SIZE)
//                        throw new OutOfMemoryError(oomeMsg);
//                    if (n >= MAX_ARRAY_SIZE - (MAX_ARRAY_SIZE >>> 1) - 1)
//                        n = MAX_ARRAY_SIZE;
//                    else
//                        n += (n >>> 1) + 1;
//                    r = Arrays.copyOf(r, n);
//                }
//                r[i++] = e;
//            }
//            return (i == n) ? r : Arrays.copyOf(r, i);
//        }
//
//        @SuppressWarnings("unchecked")
//        public final <T> T[] toArray(T[] a) {
//            long sz = map.mappingCount();
//            if (sz > MAX_ARRAY_SIZE)
//                throw new OutOfMemoryError(oomeMsg);
//            int m = (int)sz;
//            T[] r = (a.length >= m) ? a :
//                    (T[])java.lang.reflect.Array
//                            .newInstance(a.getClass().getComponentType(), m);
//            int n = r.length;
//            int i = 0;
//            for (E e : this) {
//                if (i == n) {
//                    if (n >= MAX_ARRAY_SIZE)
//                        throw new OutOfMemoryError(oomeMsg);
//                    if (n >= MAX_ARRAY_SIZE - (MAX_ARRAY_SIZE >>> 1) - 1)
//                        n = MAX_ARRAY_SIZE;
//                    else
//                        n += (n >>> 1) + 1;
//                    r = Arrays.copyOf(r, n);
//                }
//                r[i++] = (T)e;
//            }
//            if (a == r && i < n) {
//                r[i] = null; // null-terminate
//                return r;
//            }
//            return (i == n) ? r : Arrays.copyOf(r, i);
//        }
//
//        /**
//         * Returns a string representation of this collection.
//         * The string representation consists of the string representations
//         * of the collection's elements in the order they are returned by
//         * its iterator, enclosed in square brackets ({@code "[]"}).
//         * Adjacent elements are separated by the characters {@code ", "}
//         * (comma and space).  Elements are converted to strings as by
//         * {@link String#valueOf(Object)}.
//         *
//         * @return a string representation of this collection
//         */
//        public final String toString() {
//            StringBuilder sb = new StringBuilder();
//            sb.append('[');
//            Iterator<E> it = iterator();
//            if (it.hasNext()) {
//                for (;;) {
//                    Object e = it.next();
//                    sb.append(e == this ? "(this Collection)" : e);
//                    if (!it.hasNext())
//                        break;
//                    sb.append(',').append(' ');
//                }
//            }
//            return sb.append(']').toString();
//        }
//
//        public final boolean containsAll(Collection<?> c) {
//            if (c != this) {
//                for (Object e : c) {
//                    if (e == null || !contains(e))
//                        return false;
//                }
//            }
//            return true;
//        }
//
//        public final boolean removeAll(Collection<?> c) {
//            if (c == null) throw new NullPointerException();
//            boolean modified = false;
//            for (Iterator<E> it = iterator(); it.hasNext();) {
//                if (c.contains(it.next())) {
//                    it.remove();
//                    modified = true;
//                }
//            }
//            return modified;
//        }
//
//        public final boolean retainAll(Collection<?> c) {
//            if (c == null) throw new NullPointerException();
//            boolean modified = false;
//            for (Iterator<E> it = iterator(); it.hasNext();) {
//                if (!c.contains(it.next())) {
//                    it.remove();
//                    modified = true;
//                }
//            }
//            return modified;
//        }
//
//    }
//
//    /**
//     * A view of a ConcurrentHashMap as a {@link Set} of keys, in
//     * which additions may optionally be enabled by mapping to a
//     * common value.  This class cannot be directly instantiated.
//     * See {@link #keySet() keySet()},
//     * {@link #keySet(Object) keySet(V)},
//     * {@link #newKeySet() newKeySet()},
//     * {@link #newKeySet(int) newKeySet(int)}.
//     *
//     * @since 1.8
//     */
//    public static class KeySetView<K,V> extends CollectionView<K,V,K>
//            implements Set<K>, java.io.Serializable {
//        private static final long serialVersionUID = 7249069246763182397L;
//        private final V value;
//        KeySetView(ConcurrentHashMap18<K,V> map, V value) {  // non-public
//            super(map);
//            this.value = value;
//        }
//
//        /**
//         * Returns the default mapped value for additions,
//         * or {@code null} if additions are not supported.
//         *
//         * @return the default mapped value for additions, or {@code null}
//         * if not supported
//         */
//        public V getMappedValue() { return value; }
//
//        /**
//         * {@inheritDoc}
//         * @throws NullPointerException if the specified key is null
//         */
//        public boolean contains(Object o) { return map.containsKey(o); }
//
//        /**
//         * Removes the key from this map view, by removing the key (and its
//         * corresponding value) from the backing map.  This method does
//         * nothing if the key is not in the map.
//         *
//         * @param  o the key to be removed from the backing map
//         * @return {@code true} if the backing map contained the specified key
//         * @throws NullPointerException if the specified key is null
//         */
//        public boolean remove(Object o) { return map.remove(o) != null; }
//
//        /**
//         * @return an iterator over the keys of the backing map
//         */
//        public Iterator<K> iterator() {
//            Node<K,V>[] t;
//            ConcurrentHashMap18<K,V> m = map;
//            int f = (t = m.table) == null ? 0 : t.length;
//            return new KeyIterator<K,V>(t, f, 0, f, m);
//        }
//
//        /**
//         * Adds the specified key to this set view by mapping the key to
//         * the default mapped value in the backing map, if defined.
//         *
//         * @param e key to be added
//         * @return {@code true} if this set changed as a result of the call
//         * @throws NullPointerException if the specified key is null
//         * @throws UnsupportedOperationException if no default mapped value
//         * for additions was provided
//         */
//        public boolean add(K e) {
//            V v;
//            if ((v = value) == null)
//                throw new UnsupportedOperationException();
//            return map.putVal(e, v, true) == null;
//        }
//
//        /**
//         * Adds all of the elements in the specified collection to this set,
//         * as if by calling {@link #add} on each one.
//         *
//         * @param c the elements to be inserted into this set
//         * @return {@code true} if this set changed as a result of the call
//         * @throws NullPointerException if the collection or any of its
//         * elements are {@code null}
//         * @throws UnsupportedOperationException if no default mapped value
//         * for additions was provided
//         */
//        public boolean addAll(Collection<? extends K> c) {
//            boolean added = false;
//            V v;
//            if ((v = value) == null)
//                throw new UnsupportedOperationException();
//            for (K e : c) {
//                if (map.putVal(e, v, true) == null)
//                    added = true;
//            }
//            return added;
//        }
//
//        public int hashCode() {
//            int h = 0;
//            for (K e : this)
//                h += e.hashCode();
//            return h;
//        }
//
//        public boolean equals(Object o) {
//            Set<?> c;
//            return ((o instanceof Set) &&
//                    ((c = (Set<?>)o) == this ||
//                            (containsAll(c) && c.containsAll(this))));
//        }
//
//        public Spliterator<K> spliterator() {
//            Node<K,V>[] t;
//            ConcurrentHashMap18<K,V> m = map;
//            long n = m.sumCount();
//            int f = (t = m.table) == null ? 0 : t.length;
//            return new KeySpliterator<K,V>(t, f, 0, f, n < 0L ? 0L : n);
//        }
//
//        public void forEach(Consumer<? super K> action) {
//            if (action == null) throw new NullPointerException();
//            Node<K,V>[] t;
//            if ((t = map.table) != null) {
//                Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
//                for (Node<K,V> p; (p = it.advance()) != null; )
//                    action.accept(p.key);
//            }
//        }
//    }
//
//    /**
//     * A view of a ConcurrentHashMap as a {@link Collection} of
//     * values, in which additions are disabled. This class cannot be
//     * directly instantiated. See {@link #values()}.
//     */
//    static final class ValuesView<K,V> extends CollectionView<K,V,V>
//            implements Collection<V>, java.io.Serializable {
//        private static final long serialVersionUID = 2249069246763182397L;
//        ValuesView(ConcurrentHashMap18<K,V> map) { super(map); }
//        public final boolean contains(Object o) {
//            return map.containsValue(o);
//        }
//
//        public final boolean remove(Object o) {
//            if (o != null) {
//                for (Iterator<V> it = iterator(); it.hasNext();) {
//                    if (o.equals(it.next())) {
//                        it.remove();
//                        return true;
//                    }
//                }
//            }
//            return false;
//        }
//
//        public final Iterator<V> iterator() {
//            ConcurrentHashMap18<K,V> m = map;
//            Node<K,V>[] t;
//            int f = (t = m.table) == null ? 0 : t.length;
//            return new ValueIterator<K,V>(t, f, 0, f, m);
//        }
//
//        public final boolean add(V e) {
//            throw new UnsupportedOperationException();
//        }
//        public final boolean addAll(Collection<? extends V> c) {
//            throw new UnsupportedOperationException();
//        }
//
//        public Spliterator<V> spliterator() {
//            Node<K,V>[] t;
//            ConcurrentHashMap18<K,V> m = map;
//            long n = m.sumCount();
//            int f = (t = m.table) == null ? 0 : t.length;
//            return new ValueSpliterator<K,V>(t, f, 0, f, n < 0L ? 0L : n);
//        }
//
//        public void forEach(Consumer<? super V> action) {
//            if (action == null) throw new NullPointerException();
//            Node<K,V>[] t;
//            if ((t = map.table) != null) {
//                Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
//                for (Node<K,V> p; (p = it.advance()) != null; )
//                    action.accept(p.val);
//            }
//        }
//    }
//
//    /**
//     * A view of a ConcurrentHashMap as a {@link Set} of (key, value)
//     * entries.  This class cannot be directly instantiated. See
//     * {@link #entrySet()}.
//     */
//    static final class EntrySetView<K,V> extends CollectionView<K,V,Map.Entry<K,V>>
//            implements Set<Map.Entry<K,V>>, java.io.Serializable {
//        private static final long serialVersionUID = 2249069246763182397L;
//        EntrySetView(ConcurrentHashMap18<K,V> map) { super(map); }
//
//        public boolean contains(Object o) {
//            Object k, v, r; Map.Entry<?,?> e;
//            return ((o instanceof Map.Entry) &&
//                    (k = (e = (Map.Entry<?,?>)o).getKey()) != null &&
//                    (r = map.get(k)) != null &&
//                    (v = e.getValue()) != null &&
//                    (v == r || v.equals(r)));
//        }
//
//        public boolean remove(Object o) {
//            Object k, v; Map.Entry<?,?> e;
//            return ((o instanceof Map.Entry) &&
//                    (k = (e = (Map.Entry<?,?>)o).getKey()) != null &&
//                    (v = e.getValue()) != null &&
//                    map.remove(k, v));
//        }
//
//        /**
//         * @return an iterator over the entries of the backing map
//         */
//        public Iterator<Map.Entry<K,V>> iterator() {
//            ConcurrentHashMap18<K,V> m = map;
//            Node<K,V>[] t;
//            int f = (t = m.table) == null ? 0 : t.length;
//            return new EntryIterator<K,V>(t, f, 0, f, m);
//        }
//
//        public boolean add(Entry<K,V> e) {
//            return map.putVal(e.getKey(), e.getValue(), false) == null;
//        }
//
//        public boolean addAll(Collection<? extends Entry<K,V>> c) {
//            boolean added = false;
//            for (Entry<K,V> e : c) {
//                if (add(e))
//                    added = true;
//            }
//            return added;
//        }
//
//        public final int hashCode() {
//            int h = 0;
//            Node<K,V>[] t;
//            if ((t = map.table) != null) {
//                Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
//                for (Node<K,V> p; (p = it.advance()) != null; ) {
//                    h += p.hashCode();
//                }
//            }
//            return h;
//        }
//
//        public final boolean equals(Object o) {
//            Set<?> c;
//            return ((o instanceof Set) &&
//                    ((c = (Set<?>)o) == this ||
//                            (containsAll(c) && c.containsAll(this))));
//        }
//
//        public Spliterator<Map.Entry<K,V>> spliterator() {
//            Node<K,V>[] t;
//            ConcurrentHashMap18<K,V> m = map;
//            long n = m.sumCount();
//            int f = (t = m.table) == null ? 0 : t.length;
//            return new EntrySpliterator<K,V>(t, f, 0, f, n < 0L ? 0L : n, m);
//        }
//
//        public void forEach(Consumer<? super Map.Entry<K,V>> action) {
//            if (action == null) throw new NullPointerException();
//            Node<K,V>[] t;
//            if ((t = map.table) != null) {
//                Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
//                for (Node<K,V> p; (p = it.advance()) != null; )
//                    action.accept(new MapEntry<K,V>(p.key, p.val, map));
//            }
//        }
//
//    }
//
//    // -------------------------------------------------------
//
//    /**
//     * Base class for bulk tasks. Repeats some fields and code from
//     * class Traverser, because we need to subclass CountedCompleter.
//     */
//    @SuppressWarnings("serial")
//    abstract static class BulkTask<K,V,R> extends CountedCompleter<R> {
//        Node<K,V>[] tab;        // same as Traverser
//        Node<K,V> next;
//        TableStack<K,V> stack, spare;
//        int index;
//        int baseIndex;
//        int baseLimit;
//        final int baseSize;
//        int batch;              // split control
//
//        BulkTask(BulkTask<K,V,?> par, int b, int i, int f, Node<K,V>[] t) {
//            super(par);
//            this.batch = b;
//            this.index = this.baseIndex = i;
//            if ((this.tab = t) == null)
//                this.baseSize = this.baseLimit = 0;
//            else if (par == null)
//                this.baseSize = this.baseLimit = t.length;
//            else {
//                this.baseLimit = f;
//                this.baseSize = par.baseSize;
//            }
//        }
//
//        /**
//         * Same as Traverser version
//         */
//        final Node<K,V> advance() {
//            Node<K,V> e;
//            if ((e = next) != null)
//                e = e.next;
//            for (;;) {
//                Node<K,V>[] t; int i, n;
//                if (e != null)
//                    return next = e;
//                if (baseIndex >= baseLimit || (t = tab) == null ||
//                        (n = t.length) <= (i = index) || i < 0)
//                    return next = null;
//                if ((e = tabAt(t, i)) != null && e.hash < 0) {
//                    if (e instanceof ForwardingNode) {
//                        tab = ((ForwardingNode<K,V>)e).nextTable;
//                        e = null;
//                        pushState(t, i, n);
//                        continue;
//                    }
//                    else if (e instanceof TreeBin)
//                        e = ((TreeBin<K,V>)e).first;
//                    else
//                        e = null;
//                }
//                if (stack != null)
//                    recoverState(n);
//                else if ((index = i + baseSize) >= n)
//                    index = ++baseIndex;
//            }
//        }
//
//        private void pushState(Node<K,V>[] t, int i, int n) {
//            TableStack<K,V> s = spare;
//            if (s != null)
//                spare = s.next;
//            else
//                s = new TableStack<K,V>();
//            s.tab = t;
//            s.length = n;
//            s.index = i;
//            s.next = stack;
//            stack = s;
//        }
//
//        private void recoverState(int n) {
//            TableStack<K,V> s; int len;
//            while ((s = stack) != null && (index += (len = s.length)) >= n) {
//                n = len;
//                index = s.index;
//                tab = s.tab;
//                s.tab = null;
//                TableStack<K,V> next = s.next;
//                s.next = spare; // save for reuse
//                stack = next;
//                spare = s;
//            }
//            if (s == null && (index += baseSize) >= n)
//                index = ++baseIndex;
//        }
//    }
//
//    /*
//     * Task classes. Coded in a regular but ugly format/style to
//     * simplify checks that each variant differs in the right way from
//     * others. The null screenings exist because compilers cannot tell
//     * that we've already null-checked task arguments, so we force
//     * simplest hoisted bypass to help avoid convoluted traps.
//     */
//    @SuppressWarnings("serial")
//    static final class ForEachKeyTask<K,V>
//            extends BulkTask<K,V,Void> {
//        final Consumer<? super K> action;
//        ForEachKeyTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 Consumer<? super K> action) {
//            super(p, b, i, f, t);
//            this.action = action;
//        }
//        public final void compute() {
//            final Consumer<? super K> action;
//            if ((action = this.action) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    new ForEachKeyTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    action).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null;)
//                    action.accept(p.key);
//                propagateCompletion();
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class ForEachValueTask<K,V>
//            extends BulkTask<K,V,Void> {
//        final Consumer<? super V> action;
//        ForEachValueTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 Consumer<? super V> action) {
//            super(p, b, i, f, t);
//            this.action = action;
//        }
//        public final void compute() {
//            final Consumer<? super V> action;
//            if ((action = this.action) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    new ForEachValueTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    action).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null;)
//                    action.accept(p.val);
//                propagateCompletion();
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class ForEachEntryTask<K,V>
//            extends BulkTask<K,V,Void> {
//        final Consumer<? super Entry<K,V>> action;
//        ForEachEntryTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 Consumer<? super Entry<K,V>> action) {
//            super(p, b, i, f, t);
//            this.action = action;
//        }
//        public final void compute() {
//            final Consumer<? super Entry<K,V>> action;
//            if ((action = this.action) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    new ForEachEntryTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    action).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    action.accept(p);
//                propagateCompletion();
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class ForEachMappingTask<K,V>
//            extends BulkTask<K,V,Void> {
//        final BiConsumer<? super K, ? super V> action;
//        ForEachMappingTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 BiConsumer<? super K,? super V> action) {
//            super(p, b, i, f, t);
//            this.action = action;
//        }
//        public final void compute() {
//            final BiConsumer<? super K, ? super V> action;
//            if ((action = this.action) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    new ForEachMappingTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    action).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    action.accept(p.key, p.val);
//                propagateCompletion();
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class ForEachTransformedKeyTask<K,V,U>
//            extends BulkTask<K,V,Void> {
//        final Function<? super K, ? extends U> transformer;
//        final Consumer<? super U> action;
//        ForEachTransformedKeyTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 Function<? super K, ? extends U> transformer, Consumer<? super U> action) {
//            super(p, b, i, f, t);
//            this.transformer = transformer; this.action = action;
//        }
//        public final void compute() {
//            final Function<? super K, ? extends U> transformer;
//            final Consumer<? super U> action;
//            if ((transformer = this.transformer) != null &&
//                    (action = this.action) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    new ForEachTransformedKeyTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    transformer, action).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; ) {
//                    U u;
//                    if ((u = transformer.apply(p.key)) != null)
//                        action.accept(u);
//                }
//                propagateCompletion();
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class ForEachTransformedValueTask<K,V,U>
//            extends BulkTask<K,V,Void> {
//        final Function<? super V, ? extends U> transformer;
//        final Consumer<? super U> action;
//        ForEachTransformedValueTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 Function<? super V, ? extends U> transformer, Consumer<? super U> action) {
//            super(p, b, i, f, t);
//            this.transformer = transformer; this.action = action;
//        }
//        public final void compute() {
//            final Function<? super V, ? extends U> transformer;
//            final Consumer<? super U> action;
//            if ((transformer = this.transformer) != null &&
//                    (action = this.action) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    new ForEachTransformedValueTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    transformer, action).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; ) {
//                    U u;
//                    if ((u = transformer.apply(p.val)) != null)
//                        action.accept(u);
//                }
//                propagateCompletion();
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class ForEachTransformedEntryTask<K,V,U>
//            extends BulkTask<K,V,Void> {
//        final Function<Map.Entry<K,V>, ? extends U> transformer;
//        final Consumer<? super U> action;
//        ForEachTransformedEntryTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 Function<Map.Entry<K,V>, ? extends U> transformer, Consumer<? super U> action) {
//            super(p, b, i, f, t);
//            this.transformer = transformer; this.action = action;
//        }
//        public final void compute() {
//            final Function<Map.Entry<K,V>, ? extends U> transformer;
//            final Consumer<? super U> action;
//            if ((transformer = this.transformer) != null &&
//                    (action = this.action) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    new ForEachTransformedEntryTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    transformer, action).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; ) {
//                    U u;
//                    if ((u = transformer.apply(p)) != null)
//                        action.accept(u);
//                }
//                propagateCompletion();
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class ForEachTransformedMappingTask<K,V,U>
//            extends BulkTask<K,V,Void> {
//        final BiFunction<? super K, ? super V, ? extends U> transformer;
//        final Consumer<? super U> action;
//        ForEachTransformedMappingTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 BiFunction<? super K, ? super V, ? extends U> transformer,
//                 Consumer<? super U> action) {
//            super(p, b, i, f, t);
//            this.transformer = transformer; this.action = action;
//        }
//        public final void compute() {
//            final BiFunction<? super K, ? super V, ? extends U> transformer;
//            final Consumer<? super U> action;
//            if ((transformer = this.transformer) != null &&
//                    (action = this.action) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    new ForEachTransformedMappingTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    transformer, action).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; ) {
//                    U u;
//                    if ((u = transformer.apply(p.key, p.val)) != null)
//                        action.accept(u);
//                }
//                propagateCompletion();
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class SearchKeysTask<K,V,U>
//            extends BulkTask<K,V,U> {
//        final Function<? super K, ? extends U> searchFunction;
//        final AtomicReference<U> result;
//        SearchKeysTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 Function<? super K, ? extends U> searchFunction,
//                 AtomicReference<U> result) {
//            super(p, b, i, f, t);
//            this.searchFunction = searchFunction; this.result = result;
//        }
//        public final U getRawResult() { return result.get(); }
//        public final void compute() {
//            final Function<? super K, ? extends U> searchFunction;
//            final AtomicReference<U> result;
//            if ((searchFunction = this.searchFunction) != null &&
//                    (result = this.result) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    if (result.get() != null)
//                        return;
//                    addToPendingCount(1);
//                    new SearchKeysTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    searchFunction, result).fork();
//                }
//                while (result.get() == null) {
//                    U u;
//                    Node<K,V> p;
//                    if ((p = advance()) == null) {
//                        propagateCompletion();
//                        break;
//                    }
//                    if ((u = searchFunction.apply(p.key)) != null) {
//                        if (result.compareAndSet(null, u))
//                            quietlyCompleteRoot();
//                        break;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class SearchValuesTask<K,V,U>
//            extends BulkTask<K,V,U> {
//        final Function<? super V, ? extends U> searchFunction;
//        final AtomicReference<U> result;
//        SearchValuesTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 Function<? super V, ? extends U> searchFunction,
//                 AtomicReference<U> result) {
//            super(p, b, i, f, t);
//            this.searchFunction = searchFunction; this.result = result;
//        }
//        public final U getRawResult() { return result.get(); }
//        public final void compute() {
//            final Function<? super V, ? extends U> searchFunction;
//            final AtomicReference<U> result;
//            if ((searchFunction = this.searchFunction) != null &&
//                    (result = this.result) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    if (result.get() != null)
//                        return;
//                    addToPendingCount(1);
//                    new SearchValuesTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    searchFunction, result).fork();
//                }
//                while (result.get() == null) {
//                    U u;
//                    Node<K,V> p;
//                    if ((p = advance()) == null) {
//                        propagateCompletion();
//                        break;
//                    }
//                    if ((u = searchFunction.apply(p.val)) != null) {
//                        if (result.compareAndSet(null, u))
//                            quietlyCompleteRoot();
//                        break;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class SearchEntriesTask<K,V,U>
//            extends BulkTask<K,V,U> {
//        final Function<Entry<K,V>, ? extends U> searchFunction;
//        final AtomicReference<U> result;
//        SearchEntriesTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 Function<Entry<K,V>, ? extends U> searchFunction,
//                 AtomicReference<U> result) {
//            super(p, b, i, f, t);
//            this.searchFunction = searchFunction; this.result = result;
//        }
//        public final U getRawResult() { return result.get(); }
//        public final void compute() {
//            final Function<Entry<K,V>, ? extends U> searchFunction;
//            final AtomicReference<U> result;
//            if ((searchFunction = this.searchFunction) != null &&
//                    (result = this.result) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    if (result.get() != null)
//                        return;
//                    addToPendingCount(1);
//                    new SearchEntriesTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    searchFunction, result).fork();
//                }
//                while (result.get() == null) {
//                    U u;
//                    Node<K,V> p;
//                    if ((p = advance()) == null) {
//                        propagateCompletion();
//                        break;
//                    }
//                    if ((u = searchFunction.apply(p)) != null) {
//                        if (result.compareAndSet(null, u))
//                            quietlyCompleteRoot();
//                        return;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class SearchMappingsTask<K,V,U>
//            extends BulkTask<K,V,U> {
//        final BiFunction<? super K, ? super V, ? extends U> searchFunction;
//        final AtomicReference<U> result;
//        SearchMappingsTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 BiFunction<? super K, ? super V, ? extends U> searchFunction,
//                 AtomicReference<U> result) {
//            super(p, b, i, f, t);
//            this.searchFunction = searchFunction; this.result = result;
//        }
//        public final U getRawResult() { return result.get(); }
//        public final void compute() {
//            final BiFunction<? super K, ? super V, ? extends U> searchFunction;
//            final AtomicReference<U> result;
//            if ((searchFunction = this.searchFunction) != null &&
//                    (result = this.result) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    if (result.get() != null)
//                        return;
//                    addToPendingCount(1);
//                    new SearchMappingsTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    searchFunction, result).fork();
//                }
//                while (result.get() == null) {
//                    U u;
//                    Node<K,V> p;
//                    if ((p = advance()) == null) {
//                        propagateCompletion();
//                        break;
//                    }
//                    if ((u = searchFunction.apply(p.key, p.val)) != null) {
//                        if (result.compareAndSet(null, u))
//                            quietlyCompleteRoot();
//                        break;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class ReduceKeysTask<K,V>
//            extends BulkTask<K,V,K> {
//        final BiFunction<? super K, ? super K, ? extends K> reducer;
//        K result;
//        ReduceKeysTask<K,V> rights, nextRight;
//        ReduceKeysTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 ReduceKeysTask<K,V> nextRight,
//                 BiFunction<? super K, ? super K, ? extends K> reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.reducer = reducer;
//        }
//        public final K getRawResult() { return result; }
//        public final void compute() {
//            final BiFunction<? super K, ? super K, ? extends K> reducer;
//            if ((reducer = this.reducer) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new ReduceKeysTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, reducer)).fork();
//                }
//                K r = null;
//                for (Node<K,V> p; (p = advance()) != null; ) {
//                    K u = p.key;
//                    r = (r == null) ? u : u == null ? r : reducer.apply(r, u);
//                }
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    ReduceKeysTask<K,V>
//                            t = (ReduceKeysTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        K tr, sr;
//                        if ((sr = s.result) != null)
//                            t.result = (((tr = t.result) == null) ? sr :
//                                    reducer.apply(tr, sr));
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class ReduceValuesTask<K,V>
//            extends BulkTask<K,V,V> {
//        final BiFunction<? super V, ? super V, ? extends V> reducer;
//        V result;
//        ReduceValuesTask<K,V> rights, nextRight;
//        ReduceValuesTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 ReduceValuesTask<K,V> nextRight,
//                 BiFunction<? super V, ? super V, ? extends V> reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.reducer = reducer;
//        }
//        public final V getRawResult() { return result; }
//        public final void compute() {
//            final BiFunction<? super V, ? super V, ? extends V> reducer;
//            if ((reducer = this.reducer) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new ReduceValuesTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, reducer)).fork();
//                }
//                V r = null;
//                for (Node<K,V> p; (p = advance()) != null; ) {
//                    V v = p.val;
//                    r = (r == null) ? v : reducer.apply(r, v);
//                }
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    ReduceValuesTask<K,V>
//                            t = (ReduceValuesTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        V tr, sr;
//                        if ((sr = s.result) != null)
//                            t.result = (((tr = t.result) == null) ? sr :
//                                    reducer.apply(tr, sr));
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class ReduceEntriesTask<K,V>
//            extends BulkTask<K,V,Map.Entry<K,V>> {
//        final BiFunction<Map.Entry<K,V>, Map.Entry<K,V>, ? extends Map.Entry<K,V>> reducer;
//        Map.Entry<K,V> result;
//        ReduceEntriesTask<K,V> rights, nextRight;
//        ReduceEntriesTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 ReduceEntriesTask<K,V> nextRight,
//                 BiFunction<Entry<K,V>, Map.Entry<K,V>, ? extends Map.Entry<K,V>> reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.reducer = reducer;
//        }
//        public final Map.Entry<K,V> getRawResult() { return result; }
//        public final void compute() {
//            final BiFunction<Map.Entry<K,V>, Map.Entry<K,V>, ? extends Map.Entry<K,V>> reducer;
//            if ((reducer = this.reducer) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new ReduceEntriesTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, reducer)).fork();
//                }
//                Map.Entry<K,V> r = null;
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = (r == null) ? p : reducer.apply(r, p);
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    ReduceEntriesTask<K,V>
//                            t = (ReduceEntriesTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        Map.Entry<K,V> tr, sr;
//                        if ((sr = s.result) != null)
//                            t.result = (((tr = t.result) == null) ? sr :
//                                    reducer.apply(tr, sr));
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceKeysTask<K,V,U>
//            extends BulkTask<K,V,U> {
//        final Function<? super K, ? extends U> transformer;
//        final BiFunction<? super U, ? super U, ? extends U> reducer;
//        U result;
//        MapReduceKeysTask<K,V,U> rights, nextRight;
//        MapReduceKeysTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceKeysTask<K,V,U> nextRight,
//                 Function<? super K, ? extends U> transformer,
//                 BiFunction<? super U, ? super U, ? extends U> reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.reducer = reducer;
//        }
//        public final U getRawResult() { return result; }
//        public final void compute() {
//            final Function<? super K, ? extends U> transformer;
//            final BiFunction<? super U, ? super U, ? extends U> reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceKeysTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, reducer)).fork();
//                }
//                U r = null;
//                for (Node<K,V> p; (p = advance()) != null; ) {
//                    U u;
//                    if ((u = transformer.apply(p.key)) != null)
//                        r = (r == null) ? u : reducer.apply(r, u);
//                }
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceKeysTask<K,V,U>
//                            t = (MapReduceKeysTask<K,V,U>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        U tr, sr;
//                        if ((sr = s.result) != null)
//                            t.result = (((tr = t.result) == null) ? sr :
//                                    reducer.apply(tr, sr));
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceValuesTask<K,V,U>
//            extends BulkTask<K,V,U> {
//        final Function<? super V, ? extends U> transformer;
//        final BiFunction<? super U, ? super U, ? extends U> reducer;
//        U result;
//        MapReduceValuesTask<K,V,U> rights, nextRight;
//        MapReduceValuesTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceValuesTask<K,V,U> nextRight,
//                 Function<? super V, ? extends U> transformer,
//                 BiFunction<? super U, ? super U, ? extends U> reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.reducer = reducer;
//        }
//        public final U getRawResult() { return result; }
//        public final void compute() {
//            final Function<? super V, ? extends U> transformer;
//            final BiFunction<? super U, ? super U, ? extends U> reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceValuesTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, reducer)).fork();
//                }
//                U r = null;
//                for (Node<K,V> p; (p = advance()) != null; ) {
//                    U u;
//                    if ((u = transformer.apply(p.val)) != null)
//                        r = (r == null) ? u : reducer.apply(r, u);
//                }
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceValuesTask<K,V,U>
//                            t = (MapReduceValuesTask<K,V,U>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        U tr, sr;
//                        if ((sr = s.result) != null)
//                            t.result = (((tr = t.result) == null) ? sr :
//                                    reducer.apply(tr, sr));
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceEntriesTask<K,V,U>
//            extends BulkTask<K,V,U> {
//        final Function<Map.Entry<K,V>, ? extends U> transformer;
//        final BiFunction<? super U, ? super U, ? extends U> reducer;
//        U result;
//        MapReduceEntriesTask<K,V,U> rights, nextRight;
//        MapReduceEntriesTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceEntriesTask<K,V,U> nextRight,
//                 Function<Map.Entry<K,V>, ? extends U> transformer,
//                 BiFunction<? super U, ? super U, ? extends U> reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.reducer = reducer;
//        }
//        public final U getRawResult() { return result; }
//        public final void compute() {
//            final Function<Map.Entry<K,V>, ? extends U> transformer;
//            final BiFunction<? super U, ? super U, ? extends U> reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceEntriesTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, reducer)).fork();
//                }
//                U r = null;
//                for (Node<K,V> p; (p = advance()) != null; ) {
//                    U u;
//                    if ((u = transformer.apply(p)) != null)
//                        r = (r == null) ? u : reducer.apply(r, u);
//                }
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceEntriesTask<K,V,U>
//                            t = (MapReduceEntriesTask<K,V,U>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        U tr, sr;
//                        if ((sr = s.result) != null)
//                            t.result = (((tr = t.result) == null) ? sr :
//                                    reducer.apply(tr, sr));
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceMappingsTask<K,V,U>
//            extends BulkTask<K,V,U> {
//        final BiFunction<? super K, ? super V, ? extends U> transformer;
//        final BiFunction<? super U, ? super U, ? extends U> reducer;
//        U result;
//        MapReduceMappingsTask<K,V,U> rights, nextRight;
//        MapReduceMappingsTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceMappingsTask<K,V,U> nextRight,
//                 BiFunction<? super K, ? super V, ? extends U> transformer,
//                 BiFunction<? super U, ? super U, ? extends U> reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.reducer = reducer;
//        }
//        public final U getRawResult() { return result; }
//        public final void compute() {
//            final BiFunction<? super K, ? super V, ? extends U> transformer;
//            final BiFunction<? super U, ? super U, ? extends U> reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceMappingsTask<K,V,U>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, reducer)).fork();
//                }
//                U r = null;
//                for (Node<K,V> p; (p = advance()) != null; ) {
//                    U u;
//                    if ((u = transformer.apply(p.key, p.val)) != null)
//                        r = (r == null) ? u : reducer.apply(r, u);
//                }
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceMappingsTask<K,V,U>
//                            t = (MapReduceMappingsTask<K,V,U>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        U tr, sr;
//                        if ((sr = s.result) != null)
//                            t.result = (((tr = t.result) == null) ? sr :
//                                    reducer.apply(tr, sr));
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceKeysToDoubleTask<K,V>
//            extends BulkTask<K,V,Double> {
//        final ToDoubleFunction<? super K> transformer;
//        final DoubleBinaryOperator reducer;
//        final double basis;
//        double result;
//        MapReduceKeysToDoubleTask<K,V> rights, nextRight;
//        MapReduceKeysToDoubleTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceKeysToDoubleTask<K,V> nextRight,
//                 ToDoubleFunction<? super K> transformer,
//                 double basis,
//                 DoubleBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Double getRawResult() { return result; }
//        public final void compute() {
//            final ToDoubleFunction<? super K> transformer;
//            final DoubleBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                double r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceKeysToDoubleTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsDouble(r, transformer.applyAsDouble(p.key));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceKeysToDoubleTask<K,V>
//                            t = (MapReduceKeysToDoubleTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsDouble(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceValuesToDoubleTask<K,V>
//            extends BulkTask<K,V,Double> {
//        final ToDoubleFunction<? super V> transformer;
//        final DoubleBinaryOperator reducer;
//        final double basis;
//        double result;
//        MapReduceValuesToDoubleTask<K,V> rights, nextRight;
//        MapReduceValuesToDoubleTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceValuesToDoubleTask<K,V> nextRight,
//                 ToDoubleFunction<? super V> transformer,
//                 double basis,
//                 DoubleBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Double getRawResult() { return result; }
//        public final void compute() {
//            final ToDoubleFunction<? super V> transformer;
//            final DoubleBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                double r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceValuesToDoubleTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsDouble(r, transformer.applyAsDouble(p.val));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceValuesToDoubleTask<K,V>
//                            t = (MapReduceValuesToDoubleTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsDouble(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceEntriesToDoubleTask<K,V>
//            extends BulkTask<K,V,Double> {
//        final ToDoubleFunction<Map.Entry<K,V>> transformer;
//        final DoubleBinaryOperator reducer;
//        final double basis;
//        double result;
//        MapReduceEntriesToDoubleTask<K,V> rights, nextRight;
//        MapReduceEntriesToDoubleTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceEntriesToDoubleTask<K,V> nextRight,
//                 ToDoubleFunction<Map.Entry<K,V>> transformer,
//                 double basis,
//                 DoubleBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Double getRawResult() { return result; }
//        public final void compute() {
//            final ToDoubleFunction<Map.Entry<K,V>> transformer;
//            final DoubleBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                double r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceEntriesToDoubleTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsDouble(r, transformer.applyAsDouble(p));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceEntriesToDoubleTask<K,V>
//                            t = (MapReduceEntriesToDoubleTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsDouble(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceMappingsToDoubleTask<K,V>
//            extends BulkTask<K,V,Double> {
//        final ToDoubleBiFunction<? super K, ? super V> transformer;
//        final DoubleBinaryOperator reducer;
//        final double basis;
//        double result;
//        MapReduceMappingsToDoubleTask<K,V> rights, nextRight;
//        MapReduceMappingsToDoubleTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceMappingsToDoubleTask<K,V> nextRight,
//                 ToDoubleBiFunction<? super K, ? super V> transformer,
//                 double basis,
//                 DoubleBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Double getRawResult() { return result; }
//        public final void compute() {
//            final ToDoubleBiFunction<? super K, ? super V> transformer;
//            final DoubleBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                double r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceMappingsToDoubleTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsDouble(r, transformer.applyAsDouble(p.key, p.val));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceMappingsToDoubleTask<K,V>
//                            t = (MapReduceMappingsToDoubleTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsDouble(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceKeysToLongTask<K,V>
//            extends BulkTask<K,V,Long> {
//        final ToLongFunction<? super K> transformer;
//        final LongBinaryOperator reducer;
//        final long basis;
//        long result;
//        MapReduceKeysToLongTask<K,V> rights, nextRight;
//        MapReduceKeysToLongTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceKeysToLongTask<K,V> nextRight,
//                 ToLongFunction<? super K> transformer,
//                 long basis,
//                 LongBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Long getRawResult() { return result; }
//        public final void compute() {
//            final ToLongFunction<? super K> transformer;
//            final LongBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                long r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceKeysToLongTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsLong(r, transformer.applyAsLong(p.key));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceKeysToLongTask<K,V>
//                            t = (MapReduceKeysToLongTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsLong(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceValuesToLongTask<K,V>
//            extends BulkTask<K,V,Long> {
//        final ToLongFunction<? super V> transformer;
//        final LongBinaryOperator reducer;
//        final long basis;
//        long result;
//        MapReduceValuesToLongTask<K,V> rights, nextRight;
//        MapReduceValuesToLongTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceValuesToLongTask<K,V> nextRight,
//                 ToLongFunction<? super V> transformer,
//                 long basis,
//                 LongBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Long getRawResult() { return result; }
//        public final void compute() {
//            final ToLongFunction<? super V> transformer;
//            final LongBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                long r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceValuesToLongTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsLong(r, transformer.applyAsLong(p.val));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceValuesToLongTask<K,V>
//                            t = (MapReduceValuesToLongTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsLong(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceEntriesToLongTask<K,V>
//            extends BulkTask<K,V,Long> {
//        final ToLongFunction<Map.Entry<K,V>> transformer;
//        final LongBinaryOperator reducer;
//        final long basis;
//        long result;
//        MapReduceEntriesToLongTask<K,V> rights, nextRight;
//        MapReduceEntriesToLongTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceEntriesToLongTask<K,V> nextRight,
//                 ToLongFunction<Map.Entry<K,V>> transformer,
//                 long basis,
//                 LongBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Long getRawResult() { return result; }
//        public final void compute() {
//            final ToLongFunction<Map.Entry<K,V>> transformer;
//            final LongBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                long r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceEntriesToLongTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsLong(r, transformer.applyAsLong(p));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceEntriesToLongTask<K,V>
//                            t = (MapReduceEntriesToLongTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsLong(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceMappingsToLongTask<K,V>
//            extends BulkTask<K,V,Long> {
//        final ToLongBiFunction<? super K, ? super V> transformer;
//        final LongBinaryOperator reducer;
//        final long basis;
//        long result;
//        MapReduceMappingsToLongTask<K,V> rights, nextRight;
//        MapReduceMappingsToLongTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceMappingsToLongTask<K,V> nextRight,
//                 ToLongBiFunction<? super K, ? super V> transformer,
//                 long basis,
//                 LongBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Long getRawResult() { return result; }
//        public final void compute() {
//            final ToLongBiFunction<? super K, ? super V> transformer;
//            final LongBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                long r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceMappingsToLongTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsLong(r, transformer.applyAsLong(p.key, p.val));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceMappingsToLongTask<K,V>
//                            t = (MapReduceMappingsToLongTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsLong(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceKeysToIntTask<K,V>
//            extends BulkTask<K,V,Integer> {
//        final ToIntFunction<? super K> transformer;
//        final IntBinaryOperator reducer;
//        final int basis;
//        int result;
//        MapReduceKeysToIntTask<K,V> rights, nextRight;
//        MapReduceKeysToIntTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceKeysToIntTask<K,V> nextRight,
//                 ToIntFunction<? super K> transformer,
//                 int basis,
//                 IntBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Integer getRawResult() { return result; }
//        public final void compute() {
//            final ToIntFunction<? super K> transformer;
//            final IntBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                int r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceKeysToIntTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsInt(r, transformer.applyAsInt(p.key));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceKeysToIntTask<K,V>
//                            t = (MapReduceKeysToIntTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsInt(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceValuesToIntTask<K,V>
//            extends BulkTask<K,V,Integer> {
//        final ToIntFunction<? super V> transformer;
//        final IntBinaryOperator reducer;
//        final int basis;
//        int result;
//        MapReduceValuesToIntTask<K,V> rights, nextRight;
//        MapReduceValuesToIntTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceValuesToIntTask<K,V> nextRight,
//                 ToIntFunction<? super V> transformer,
//                 int basis,
//                 IntBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Integer getRawResult() { return result; }
//        public final void compute() {
//            final ToIntFunction<? super V> transformer;
//            final IntBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                int r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceValuesToIntTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsInt(r, transformer.applyAsInt(p.val));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceValuesToIntTask<K,V>
//                            t = (MapReduceValuesToIntTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsInt(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceEntriesToIntTask<K,V>
//            extends BulkTask<K,V,Integer> {
//        final ToIntFunction<Map.Entry<K,V>> transformer;
//        final IntBinaryOperator reducer;
//        final int basis;
//        int result;
//        MapReduceEntriesToIntTask<K,V> rights, nextRight;
//        MapReduceEntriesToIntTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceEntriesToIntTask<K,V> nextRight,
//                 ToIntFunction<Map.Entry<K,V>> transformer,
//                 int basis,
//                 IntBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Integer getRawResult() { return result; }
//        public final void compute() {
//            final ToIntFunction<Map.Entry<K,V>> transformer;
//            final IntBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                int r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceEntriesToIntTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsInt(r, transformer.applyAsInt(p));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceEntriesToIntTask<K,V>
//                            t = (MapReduceEntriesToIntTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsInt(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    @SuppressWarnings("serial")
//    static final class MapReduceMappingsToIntTask<K,V>
//            extends BulkTask<K,V,Integer> {
//        final ToIntBiFunction<? super K, ? super V> transformer;
//        final IntBinaryOperator reducer;
//        final int basis;
//        int result;
//        MapReduceMappingsToIntTask<K,V> rights, nextRight;
//        MapReduceMappingsToIntTask
//                (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
//                 MapReduceMappingsToIntTask<K,V> nextRight,
//                 ToIntBiFunction<? super K, ? super V> transformer,
//                 int basis,
//                 IntBinaryOperator reducer) {
//            super(p, b, i, f, t); this.nextRight = nextRight;
//            this.transformer = transformer;
//            this.basis = basis; this.reducer = reducer;
//        }
//        public final Integer getRawResult() { return result; }
//        public final void compute() {
//            final ToIntBiFunction<? super K, ? super V> transformer;
//            final IntBinaryOperator reducer;
//            if ((transformer = this.transformer) != null &&
//                    (reducer = this.reducer) != null) {
//                int r = this.basis;
//                for (int i = baseIndex, f, h; batch > 0 &&
//                        (h = ((f = baseLimit) + i) >>> 1) > i;) {
//                    addToPendingCount(1);
//                    (rights = new MapReduceMappingsToIntTask<K,V>
//                            (this, batch >>>= 1, baseLimit = h, f, tab,
//                                    rights, transformer, r, reducer)).fork();
//                }
//                for (Node<K,V> p; (p = advance()) != null; )
//                    r = reducer.applyAsInt(r, transformer.applyAsInt(p.key, p.val));
//                result = r;
//                CountedCompleter<?> c;
//                for (c = firstComplete(); c != null; c = c.nextComplete()) {
//                    @SuppressWarnings("unchecked")
//                    MapReduceMappingsToIntTask<K,V>
//                            t = (MapReduceMappingsToIntTask<K,V>)c,
//                            s = t.rights;
//                    while (s != null) {
//                        t.result = reducer.applyAsInt(t.result, s.result);
//                        s = t.rights = s.nextRight;
//                    }
//                }
//            }
//        }
//    }
//
//    // Unsafe mechanics
//    private static final sun.misc.Unsafe U;
//    private static final long SIZECTL;
//    private static final long TRANSFERINDEX;
//    private static final long BASECOUNT;
//    private static final long CELLSBUSY;
//    private static final long CELLVALUE;
//    private static final long ABASE;
//    private static final int ASHIFT;
//
//    static {
//        try {
//            U = sun.misc.Unsafe.getUnsafe();
//            Class<?> k = ConcurrentHashMap18.class;
//            SIZECTL = U.objectFieldOffset
//                    (k.getDeclaredField("sizeCtl"));
//            TRANSFERINDEX = U.objectFieldOffset
//                    (k.getDeclaredField("transferIndex"));
//            BASECOUNT = U.objectFieldOffset
//                    (k.getDeclaredField("baseCount"));
//            CELLSBUSY = U.objectFieldOffset
//                    (k.getDeclaredField("cellsBusy"));
//            Class<?> ck = CounterCell.class;
//            CELLVALUE = U.objectFieldOffset
//                    (ck.getDeclaredField("value"));
//            Class<?> ak = Node[].class;
//            ABASE = U.arrayBaseOffset(ak);
//            int scale = U.arrayIndexScale(ak);
//            if ((scale & (scale - 1)) != 0)
//                throw new Error("data type scale not a power of two");
//            ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
//        } catch (Exception e) {
//            throw new Error(e);
//        }
//    }
//}
